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==Part I The Early Development to the End of the Third Day==
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=Chapter III Outline of Development, Orientation, Chronology=
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The preceding chapters have traced the development up to the time of laying. The formation of the germ-layers has begun; and the stage of development is fairly definite, though not absolutely constant. When the egg cools, after laying, the development ceases, but is renewed when the temperature is raised to the required degree by incubation.
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On the surface of the volk is a whitish disc about 4 mm. in diameter, known as the blastoderm. Edwards gives the average diameter of the unincubated blastoderm (59 eggs) as 4.41 mm., of the area pellucida (50 eggs) as 2.51 mm. The central part of the blastoderm is more transparent and is hence known as the area pellucida; beneath it is the subgerminal cavity. The less transparent periphery is known as the area opaca. In the course of development the embryo, and the embryonic membranes which serve for the protection, respiration, and nutrition of the embryo, arise from the blastoderm.
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The embryo proper arises within the area pellucida, which becomes pear-shaped as the embryo forms; the remainder of the blastoderm beyond the embryo is extra-embryonic. From it arise the embryonic membranes known as the amnion, chorion, and yolk-sac. The allantois (Fig. 33 B) arises as an outgrowth from the hind-gut of the embryo, and spreads within the extraembryonic body-cavity; it thus becomes an extra-embryonic membrane secondarily. The growth of the embryo and of the extra-embryonic blastoderm are distinct, though interdependent, processes going on at the same time.
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During the first four days of development the blastoderm spreads very rapidly (Figs. 32 and 33). 'Thus on the fourth day (Fig. 33 A) the greater portion of the yolk is already covered. Thereafter the overgrowth of the yolk proceeds much more slowly (cf. Fig. 33 B). In the opaque area there arise, as concentric zones, the area vasculosa distinguished by its blood-vessels and the area vitellina, which may be divided into inner and outer zones (Figs. 32 and 33). The development of the embryo during the same period is indicated in the same figures.
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Fig. 32. — A. Hen's egg at about the twenty-sixth hour of incubation, to show the zones of the blastoderm and the orientation of the embryo with reference to the axis of the shell. (After Duval.) B. Yolk of hen's egg incubated about 50 hours to show the extent of overgrowth of the blastoderm. (After Duval.)
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A. C, Air chamber, a. p., Area pellucida. a. v., Area vasculosa. a. v. e., Area vitellina externa, a. v. i., Area vitellina interna. Y., Uncovered portion of yolk.
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The blastoderm early becomes divided in two layers as far as the margin of the vascular area. The outer layer, known as the somatopleure, is continuous with the body-wall, which is open ventrally in the young embryo. The inner one, known as the splanchnopleure, is continuous with the wall of the intestine which is likewise open ventrally. The space between these two membranes, the extra-embryonic body-cavity, is continuous with the body-cavity of the embryo. Ultimately, the splitting of the blastoderm is carried around the entire yolk, so that the latter is enclosed in a separate sac of the splanchnopleure, the yolk-sac, which is connected by a stalk, the yolk-stalk, to the intestine of the embryo. This stalk runs through an opening in the ventral body-wall, the umbilicus, where the amnion, which has developed from the extra-embryonic somatopleure, joins the body-wall (Fig. 33 B).
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About the nineteenth day of incubation the yolk-sac is drawn into the body-cavity through the umbiUcus, which thereupon closes. The young chick usually hatches on the twenty-first day. Orientation. It is an interesting and important fact that the embryo appears in a definite relation to the line drawn through the axis of the entire egg, or to the line joining the bases of the two chalazse, which is usually the same thing. If the egg be placed as in Fig. 32 A, with the blunt end to the left, the head of the embryo will be found directed away from the observer when the blastoderm is above; the left side of the embryo is therefore towards the broad end, and the right side towards the narrow end of the egg. According to Duval this orientation is found in about 98.5% of eggs: of 166 eggs observed, in which the embryo was formed, Duval found 124 oriented exactly in this manner, 39 in which the axis of the embryo was slightly oblique, 2 in which the head was towards the broad end, and 1 in which the usual position was completely inverted. In the pigeon's egg the orientation of the embryo is equally definite, but slightly different. The axis of the embryo cuts the axis of the entire egg at an angle of about 45°, the head of the embryo being directed away from the observer to the right, when the broad end of the egg is to the observer's left as in Fig. 32 A.
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Fig. 33. — A. Yolk of hen's egg incubated 84 hours. (After Duval.) B. Embryo and membranes of the hen's egg on the seventh day of incubation. (After Duval.)
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AL, AUantois. Am., Amnion, a. v., (in B) Area vitellina. E., Embryo. S. t., Sinus terminalis. Other Abbreviations as in Fig. 32.
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The definiteness of orientation of the embryo with reference to the axis of the egg enables one to distinguish anterior and posterior ends of the blastoderm before there is any trace of an embryo; and while there is no possibility of orientation by examination of the blastoderm itself, or when such orientation is otherwise extremely difficult. By the method of orienting the blastoderm w^ith reference to the axis of the shell, observers have been able to discover important features of the early development which would otherwise, no doubt, have escaped observation The relation is of interest in other respects discussed in their appropriate places. (See p. 15.)
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==Chronology (Classification of Stages)==
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The development of an animal is an absolutely continuous process, but for purposes of description it is necessary to fix certain stages for comparison with those that precede and those that follow. Each stage has a certain position in the continuous process, and the correct arrangement of stages is therefore a sine qua non for their correct interpretation. This may seem a very simple matter seeing that development is in general from the more simple to the more complex. And it would be so if it were not for the fact that embryonic stages, like the adult individuals of a species, vary more or less, so that no one embryo is ever exactly like another. These embryonic variations involve (1) the rate of development of the whole embryo, so that at a given time in the process no two embryos are in exactly the same stage; (2) the relative rates of development of different organs; (3) the size of the embryo, for embryos of the same stage of development may vary somewhat in size.
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Although the total period of incubation is fairly constant in the hen's egg, about twenty-one days, yet there is great variation in the grade of development of embryos of the same age, especially during the first week. This is due to two main factors: first, variation in the latent period, that is the time necessar}^ to start the development of the cooled blastoderm after the egg is put into the incubator, and second, to variation in the temperature of incubation. Individual eggs may vary in rate of development when these two factors are constant, but this difference is relatively slight. Other things being equal, the latent period varies with the freshness of the egg; it is relatively short in eggs that are newly laid, and long in eggs that have remained quiescent some time after laying. It is obvious that the latent period will form a more considerable portion of the entire time of incubation in early than in late stages. Hence the difficulty of classifying embryos, particularly in the first four or five days of incubation, by period of incubation. Eggs procured from dealers usually show such great variations in degree of development, at the same time of incubation, that it is quite impossible to grade them with any high degree of accuracy by time of incubation. It is statf'd also that the rate of development varies considerably at different seasons, other factors being constant. But this has not been found to be a serious matter in my own experience.
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Variations in temperature, either above or below the normal, also seriously affect the rate of development, and produce abnormalities when extreme. If the temperature be too low, the rate is slower than normal; if too high, the rate increases up to a certain point, beyond which the egg is killed.
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The physiological zero, that is the temperature below which the blastoderm undergoes no development whatever, has been estimated differently by different authors. Some place it at about 28° C, others at about 25°; Edwards places it as low as 20-21° C. At the last temperature, apparently, a small percentage of eggs will develop in the course of several days to an early stage of the primitive streak, but most eggs show no perceptible development. In very warm weather, therefore, the atmospheric temperature m.ay be sufficient to start eggs. The following table is given by Davenport based on Fere's work:
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Temperature .34° 35° 36° 37° 38° 39° 40° 41°
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Index of Development 0.65 0.80 0.72 1.00 1.06 1.25 1.51
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The index of development represents the proportion that the average development at a given temperature in a given time bears to the normal development {i.e., development at the normal temperature for the same time). There is an increase in the rate up to 41°; a maximum temperature, which cannot be much above 41°, causes the condition of heat-rigor and death.
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There would seem to be no better way to determine the normal temperature for incubation than by measuring the temperature of eggs incubated by the hen throughout the entire period of incubation. This has been done very carefully by Eyclesh3mier, who finds the internal temperature of such eggs to be as follows:
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Day of incubation
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1
 +
 +
 +
2
 +
 +
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3
 +
 +
 +
4
 +
 +
 +
5
 +
 +
 +
Temperature of hen
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 +
102.2
 +
 +
 +
103.0
 +
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 +
103.5
 +
 +
 +
104.0
 +
 +
 +
103.8
 +
 +
 +
Temperature of egg
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 +
 +
98.0
 +
 +
 +
100.2
 +
 +
 +
100.5
 +
 +
 +
100.5
 +
 +
 +
100.4
 +
 +
 +
Day of incubation
 +
 +
 +
6
 +
 +
 +
7
 +
 +
 +
8
 +
 +
 +
9
 +
 +
 +
10
 +
 +
 +
Temperature of hen
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 +
 +
105.0
 +
 +
 +
104.6
 +
 +
 +
104.5
 +
 +
 +
105.0
 +
 +
 +
105.0
 +
 +
 +
Temperature of egg
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 +
 +
101.0
 +
 +
 +
101.8
 +
 +
 +
102.5
 +
 +
 +
101.6
 +
 +
 +
102.0
 +
 +
 +
Day of incubation
 +
 +
 +
11
 +
 +
 +
12
 +
 +
 +
13
 +
 +
 +
14
 +
 +
 +
15
 +
 +
 +
Temperature of hen
 +
 +
 +
104.8
 +
 +
 +
105.2
 +
 +
 +
104.5
 +
 +
 +
105.0
 +
 +
 +
105.2
 +
 +
 +
Temperature of egg
 +
 +
 +
101.8
 +
 +
 +
102.2
 +
 +
 +
102.0
 +
 +
 +
102.5
 +
 +
 +
102.0
 +
 +
 +
Day of incubation
 +
 +
 +
16
 +
 +
 +
17
 +
 +
 +
18
 +
 +
 +
19
 +
 +
 +
20
 +
 +
 +
Temperature of hen
 +
 +
 +
105.0
 +
 +
 +
104.6
 +
 +
 +
104.8
 +
 +
 +
104.5
 +
 +
 +
104.5
 +
 +
 +
 +
Temperature of egg 103.0 102.4 103.0 103.0 103.0
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The temperature of the hen is seen to be somewhat higher than that of the eggs. In an artificial incubator where 85 % of the fertile eggs hatched on the twentieth and twenty-first da3^s, the temperatures were as follows:
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Day of incubation Temperature of incubator Temperature of egg
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Day of incubation Temperature of incubator Temperature of egg
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Day of incubation Temperature of incubator Temperature of egg
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Day of incubation Temperature of incubator Temperature of egg
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It would be possible then to establish a normal rate of development, by using perfectly fresh eggs incubated at a normal temperature. In practice I have found that the times given in Duval's atlas are approximately normal, and these are, therefore, adopted so far as given. But even under the best conditions the variations are sufficient to prevent close grading of stages by time of incubation in the first three days. This may be due to differences in the grade of development at the time of laying, owing to varia
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1
 +
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2
 +
 +
 +
3
 +
 +
 +
4
 +
 +
 +
5
 +
 +
 +
102.0
 +
 +
 +
102.0
 +
 +
 +
103.0
 +
 +
 +
102.0
 +
 +
 +
102.5
 +
 +
 +
99.5
 +
 +
 +
100.0
 +
 +
 +
101.0
 +
 +
 +
100.5
 +
 +
 +
100.5
 +
 +
 +
6
 +
 +
 +
7
 +
 +
 +
8
 +
 +
 +
9
 +
 +
 +
10
 +
 +
 +
103.0
 +
 +
 +
102. 5
 +
 +
 +
102.0
 +
 +
 +
103.0
 +
 +
 +
103.5
 +
 +
 +
101.0
 +
 +
 +
100.0
 +
 +
 +
100.0
 +
 +
 +
101.0
 +
 +
 +
101.5
 +
 +
 +
11
 +
 +
 +
12
 +
 +
 +
13
 +
 +
 +
14
 +
 +
 +
15
 +
 +
 +
103.0
 +
 +
 +
103.5
 +
 +
 +
104.0
 +
 +
 +
103.5
 +
 +
 +
104.0
 +
 +
 +
101.5
 +
 +
 +
101.8
 +
 +
 +
102.0
 +
 +
 +
102.5
 +
 +
 +
103.0
 +
 +
 +
16
 +
 +
 +
17
 +
 +
 +
18
 +
 +
 +
19
 +
 +
 +
20
 +
 +
 +
104.5
 +
 +
 +
104.0
 +
 +
 +
103.5
 +
 +
 +
104.0
 +
 +
 +
104.5
 +
 +
 +
103.0
 +
 +
 +
103.0
 +
 +
 +
102.5
 +
 +
 +
102.5
 +
 +
 +
103.5
 +
 +
 +
 +
tioRS in the time of development in the oviduct and uterus, or to slow development before incubation in warm weather, or to individual variation. It becomes necessary, therefore, to find some other system. The method followed by a considerable number of investigators, namely to classify by the number of somites, has been found to be best between about the twentieth and ninetv-sixth hours of incubation. In the table which follows, therefore, this method of classification is used. For the sake of brevity throughout the book a stage reckoned by the number of somites will be w^ritten 1 s, 2 s, 3 s, etc. It is true that the relative rate of the development of organs varies slightly. Nevertheless, classification by number of somites is unquestionably the most exact method up to the end of the fourth day at least. Beyond this stage the method is difficult to apply, and after about the sixth day the number of somites becomes constant. After the fourth day the time of incubation is usually a sufficiently exact criterion for most purposes: the latent period has become a relatively inconsiderable fraction of the whole time of incubation, and the embryos that survive, assuming fresh eggs and normal temperature of incubation, are in about the same stage of development.
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Classification of embryos by length is a favorite method particularly in Germany, and it offers many advantages in the case of some animals; under many conditions it is the only available method. But it offers considerable difficulties, the most serious of which come from the varying degrees of curvature of the embryo. In early stages of the chick, for instance, up to about 12 s, the total length of the embryonic axis may be measured, for the embryo is approximately straight. The cranial flexure then begins to appear, and slowly increases to a right angle; during this period there may be an actual reduction in length of the embryo (cf. table, 14-16 s). Conditions are also complicated by the fact that the head of the embryo is turning on its left side at the same time. The cervical flexure then appears and causes a second reduction of the total length (cf. table 2932 s). Later still the curvature of the trunk and particularly of the tail develops in somewhat varying degrees and makes bad matters worse. After these flexures are formed, let us say at about eighty hours in the chick, it is customary to take the so-called neck-tail measurement, that is, from the cervical flexure to the apex of the tail flexure. But even then it is questionable if this measurement is as accurate a means of classification as the age of normally incubated embryos; particularly as the cervical flexure is secondarily eliminated by raising of the head. It is probable that the measurement from the tip of the head to the apex of the cranial flexure (head-length) would be best for classification of chick-embryos by measurement. This dimension may be readily taken, after the cranial flexure begins, throughout the entire period of incubation. However, it has been relatively little used up to the present time.
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The following tables give the chronology of development up to the end of the fourth day, the period usually covered in laboratory courses. For the later chronology the student is referred to Keibel and Abraham's Normaltafeln zur Entwickelungsgeschichte des Huhnes (Gallus domesticus), Jena, Gustav Fischer, 1900. In the various chapters of Part II, the later chronology of the various organs is given here and there throughout the text. It is believed that these references will be sufficient on the Avhole to enable the student to determine what embryos to select for the desired stage of most organs. The tables have been made practically continuous from 1 s up to 41s, because these cover the period of development in which the primordia of most organs are formed. They have been constructed mostly from entire mounts. The corresponding tables in Keibel and Abraham's work are noted by number in the right-hand column.
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Chronological Tables of the Development of the Chick
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I. Before Laying:
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1. Maturation and fertilization; found in the oviduct above the isthmus.
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2. Early cleavage up to about the thirty-two celled stage found in the isthmus of the oviduct during the formation of the shellmembrane (Patterson) .
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3. Later cleavage, formation of periblast and entoderm, etc., found in the uterus up to time of laying. Data for the pigeon given in Chapter II; see legends to figures.
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II. Incubation to Formation of the First Somite:
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The period may be divided in three parts: (1) before the appearance of the primitive streak; (2) primitive streak formed but no head process; (3) after the appearance of the head-process. These stages may be subdivided by time or by length of the primitive streak.
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 +
 +
 +
 +
,s
 +
 +
 +
.,,<™.
 +
 +
 +
 +
 +
 +
 +
9-j.mni.
 +
 +
 +
Mfdullary folda t1««l
 +
 +
 +
voide
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
Pure irut (luKd aboul
 +
 +
 +
 +
 +
b.il>a of bean begun
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 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
"
 +
 +
 +
'"
 +
 +
 +
es
 +
 +
 +
LIS mm.
 +
 +
 +
' lDu.Bl
 +
 +
 +
 +
 +
o*j mm.
 +
 +
 +
Mtdullary r<ild> clOKd
 +
 +
 +
[>rimaTT oplic
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
'Dre-uul doKd about
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 +
 +
 +
 +
Fuilon of Ul. haira of bean incomplete
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 +
 +
 +
Bel-een . ind 18
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 +
 +
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 +
 +
 +
 +
 +
 +
 +
 +
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Mflullary lolds ilowd
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 +
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Primarr
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 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
FDre.4tul [la»d about
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 +
 +
 +
 +
Septum between halyo
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
tej
 +
 +
 +
«s
 +
 +
 +
 +
 +
oa,i mm.
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 +
 +
 +
 +
ol heart rupturing
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 +
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 +
 +
 +
 +
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 +
 +
 +
 +
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,.,
 +
 +
 +
lit nun.
 +
 +
 +
houn iDunI)
 +
 +
J boun
 +
 +
 +
^mlndlcatiaBolcnnlil OdUrt
 +
 +
litht cnniil Oeiun
 +
 +
 +
o.i» mm.
 +
 +
 +
da dculy iadicainl
 +
 +
|.liD[ of dOSDg
 +
 +
 +
Opi. to. nol conjuiclfd .1) ba»
 +
 +
Slighi ton > "b^ ol opl in
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
Foregul do«d aboul
 +
 +
 +
 +
 +
Henri bent lUghlly lo right
 +
 +
He.in bent lo right
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 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
and™
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14 s
 +
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»»■
 +
 +
 +
 +
ighi maitl IttiuK
 +
 +
 +
Aboul oj6
 +
 +
 +
Iic»ll» Jospdr^N'nuo
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 +
Constrlttian al biMol
 +
 +
 +
Shjlloff pli
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 +
 +
 +
 +
 +
 +
 +
 +
Fir« rtKeroJ cicfl In. metU enlodetm
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 +
 +
 +
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Heart beat lo right
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 +
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 +
 +
U
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'"
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 +
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.TratllT°'m^ """"
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bX'nd & Iran
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>(S
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counuav™
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 +
 +
 +
ad b((ln> to lure on
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 +
 +
Atau. 0,
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 +
 +
 +
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Primaiy va.
 +
 +
 +
D«p, bul
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 +
 +
 +
 +
 +
 +
 +
 +
urc-gul doMd 1.4 mm.
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 +
 +
 +
 +
Uott allgblly 5-ibapcd
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 +
 +
 +
 +
leadfold coven nlremc
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 +
 +
 +
 +
 +
 +
jj
 +
 +
 +
iJI
 +
 +
 +
 +
 +
 +
 +
Ihclcllilde
 +
 +
 +
 +
 +
 +
 +
«5l'USt
 +
 +
 +
inde opcu
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
tip ol head
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
iDdicJled
 +
 +
 +
Hibcd
 +
 +
 +
pit
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
16 s
 +
 +
 +
mn, M „t„un.
 +
 +
 +
a boun
 +
 +
 +
Jk. .jS
 +
 +
 +
 +
 +
LAaisS
 +
 +
 +
UktisS
 +
 +
 +
UluiiS
 +
 +
 +
 +
 +
 +
 +
 +
 +
Fort-gut clc»] 1.1 mm.
 +
 +
 +
 +
 +
Like IS S
 +
 +
 +
 +
 +
lead-fold co.m (niirr
 +
 +
 +
 +
 +
 +
 +
•J
 +
 +
 +
0>4
 +
 +
 +
 +
 +
lakcn of Ociura
 +
 +
 +
(Du«l)
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
focebnmrwuo
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
.,s
 +
 +
 +
.„...
 +
 +
 +
 +
 +
?^^K-?J33'""
 +
 +
 +
 +
 +
LikruS, RoolofhJnd linlD becoming Ihln
 +
 +
 +
"IS
 +
 +
 +
UkcisS
 +
 +
 +
 +
 +
 +
 +
 +
 +
Second vistenil deli
 +
 +
 +
 +
 +
-■h.ipe of heart (lightly
 +
 +
 +
 +
 +
-Jead-fold coven lo olic region tunujuaily long)
 +
 +
 +
 +
 +
 +
 +
180 10 go
 +
 +
 +
,6
 +
 +
 +
■ss
 +
 +
 +
9 mm. pealBI Imgih
 +
 +
 +
 +
 +
Dlin hod mure Ikui hill luiMd DO Wl side
 +
 +
 +
^-^r^ts
 +
 +
 +
"QiLUriction appon bcl.c^n di- and leleo
 +
 +
■^sa
 +
 +
 +
Like II S
 +
 +
 +
 +
 +
 +
 +
 +
 +
Lenmb ol loregul 1 1 mm. Two iiKenJ (utnin. .liU closed
 +
 +
 +
 +
 +
-ihape of bean my Indlcuied
 +
 +
 +
 +
 +
lead fold conn anlerior
 +
 +
put of hind brain
 +
 +
 +
 +
 +
Mandibular archa begto loprojta
 +
 +
 +
"
 +
 +
 +
5.P
 +
 +
 +
,r,.s
 +
 +
 +
-S mm. urialcU length
 +
 +
 +
4 houn IUuvbI)
 +
 +
 +
udrullyluniBllaltli. Cnnlul and iin-icol ncnira rouodri ob
 +
 +
 +
 +
 +
 +
'"Sa
 +
 +
 +
Sllfhl nar = s
 +
 +
deep pit
 +
 +
 +
 +
 +
 +
 +
Na indioillDa ol hypopbi-ai
 +
 +
 +
.luough
 +
 +
 +
 +
 +
\unculo i-enlricubir Ditunnndicaiedbyoon.
 +
 +
 +
 +
 +
Like 18 S
 +
 +
 +
 +
 +
 +
 +
'*
 +
 +
 +
OS
 +
 +
 +
..s
 +
 +
 +
1„7.ES.»
 +
 +
 +
 +
 +
.elLlumrdloBlhlDmllt Cr.ni.1 (tuure-riibi anilt.itf.neiujmr)
 +
 +
Only In lail
 +
 +
 +
^j^!J!^bJr
 +
 +
 +
"sill'
 +
 +
 +
olpi.
 +
 +
 +
 +
 +
 +
 +
Hypophi-iii barely InHi
 +
 +
ihrouKh
 +
 +
jd Yi*. pouch Kcn
 +
 +
 +
 +
 +
I'tnliiculai loop noir vcnlnl ID »ur.-«n.
 +
 +
 +
 +
 +
™"""""
 +
 +
 +
 +
 +
Sudden venlrally lumed neiure ol trunk .boui 8th wmiie (due 10
 +
 +
 +
»*-3J
 +
 +
 +
»»
 +
 +
 +
...
 +
 +
 +
""
 +
 +
 +
 +
.ifllurncdloi-flinmlle. Cr.oljinau«al"UI* r. anilc. Mr., (tuui.
 +
 +
vm .fi»hi
 +
 +
 +
S'U
 +
 +
 +
«IM«»S
 +
 +
 +
»^™j, sr
 +
 +
 +
Ukt 11 S
 +
 +
 +
 +
 +
 +
 +
like 11 S
 +
 +
 +
Lenglh ol lore-gut t-J mm.olhcmiKJikeiiS
 +
 +
 +
 +
 +
Uke >i S
 +
 +
 +
 +
 +
tleadlold CTOHO id ni ani pouch nod id «
 +
 +
 +
 +
 +
 +
 +
 +
'a
 +
 +
J6»
 +
 +
 +
fjS
 +
 +
 +
J, T mm, gntUM fcnph
 +
 +
 +
 +
 +
jrviol nciun >nitc nl
 +
 +
 +
D uil bud
 +
 +
 +
Uk. a.S
 +
 +
 +
 +
 +
Moulholpil
 +
 +
 +
 +
 +
 +
 +
vi^naliaa In ftoDI Dl
 +
 +
 +
Lenglh ol lore-gut 1 ij
 +
 +
«S'riy"pertaraie4"m
 +
 +
 +
 +
 +
Like 31 S,
 +
 +
 +
 +
 +
■Jead-fnld covem lo lolh
 +
 +
 +
 +
 +
Tail. fold barely indlcaled
 +
 +
 +
iS-.i»
 +
 +
 +
J6j
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
iraoj
 +
 +
 +
 +
 +
 +
oral plate
 +
 +
 +
upper angle
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
■iiuuled
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
<i.i mm, (TtaloJ kniib
 +
 +
 +
 +
 +
.crriol nenire lite ijS.
 +
 +
 +
n tail bud
 +
 +
 +
 +
 +
Iduiniai
 +
 +
 +
Rebii«ly
 +
 +
 +
 +
 +
nalioninNo.jSi(liSl
 +
 +
 +
"^^^pllTfl^,"^^
 +
 +
 +
Lenilh nl lute-gul about
 +
 +
 +
 +
 +
Apei of i-Hilriclc vcnlnl
 +
 +
 +
 +
 +
^"t!^"™""**
 +
 +
 +
 +
 +
NolaU-fold
 +
 +
 +
 +
'
 +
 +
 +
 +
M-»» S
 +
 +
 +
iitlan> n[ tnin mnrc
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
U^n™. n«hl "^k
 +
 +
 +
 +
 +
 +
 +
iliUopcn
 +
 +
 +
oponingol SUml"'^
 +
 +
 +
 +
 +
 +
 +
lion in (funl ol oral pbU
 +
 +
 +
 +
 +
 +
 +
Two complete aoftlc arches
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
.. s
 +
 +
 +
6*«™.p«i«.i«.rh
 +
 +
 +
a houn
 +
 +
 +
di^.l',"™cl ""
 +
 +
 +
■> tall bud
 +
 +
 +
llkc«-.jS
 +
 +
 +
louth. ol
 +
 +
 +
yke.4-.1S
 +
 +
 +
 +
 +
\o epiphnii
 +
 +
 +
Same ai 14-aJ S
 +
 +
 +
»mc a. 14-1; S
 +
 +
 +
 +
 +
Sam.aa«-.^S. ^^^^ archB-^fl^d?*"""
 +
 +
 +
 +
 +
rtndlold cover. 10 171b
 +
 +
 +
 +
 +
Tall-fold indicaled
 +
 +
 +
 +
 +
049
 +
 +
 +
 +
 +
,™n.,g™,«nr«„h
 +
 +
 +
9 houn
 +
 +
 +
epiuilk fluura •llihlly ICB Ihan ixHCcUni
 +
 +
 +
nun bud
 +
 +
 +
 +
 +
toulh ol
 +
 +
 +
 +
 +
 +
 +
No cpipbtiii
 +
 +
 +
"E?^ '-'"■!
 +
 +
 +
d ri«*ral pouch ndl deielo[cd. Thyroid and lung divauoili
 +
 +
 +
 +
 +
Two complelE aortic arehu- Third nearly
 +
 +
 +
 +
 +
lead-fold coven to >otl> lomite
 +
 +
 +
 +
 +
Tail bud projecu behind Hlnd-gul lorma n bay
 +
 +
 +
 +
 +
Ji8
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
"So"
 +
 +
 +
 +
 +
 +
 +
 +
Hcll muked
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
H^^o
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
icf
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
a , mm palru Imilh
 +
 +
 +
 +
 +
"crvlcal Ituurt man
 +
 +
 +
 +
 +
 +
 +
Mouih ol
 +
 +
 +
OHe KBcIe
 +
 +
 +
rUckenlns
 +
 +
 +
Epiph,Ti. , iMTTU >liRht
 +
 +
 +
Same as ,7 S
 +
 +
 +
'.aztir.sii-
 +
 +
 +
 +
rhicT complete aortic
 +
 +
 +
 +
 +
FalJ-fold formed . con
 +
 +
Form. <maU side o|in
 +
 +
 +
 +
 +
4j
 +
 +
 +
4'
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
'p^cillSf,
 +
 +
 +
•Imuil
 +
 +
 +
0( MIO dem. No
 +
 +
 +
 +
 +
 +
 +
 +
 +
uilhn
 +
 +
 +
 +
 +
11°^ fX'" "u^
 +
 +
 +
pouch
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
diaed
 +
 +
 +
 +
 +
tn"^""
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
»mite"""
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
-., mm. nW" """
 +
 +
 +
 +
 +
UVe i« S
 +
 +
 +
 +
 +
 +
 +
Like iB S
 +
 +
 +
Like » S
 +
 +
 +
UkcittS
 +
 +
 +
No cplpb^Ul
 +
 +
 +
Same M ay
 +
 +
 +
JkeiH. Oml membrane
 +
 +
 +
 +
 +
Thn» complele aortic arcbci
 +
 +
 +
Bud3olhlnd limba Indialed by thickening
 +
 +
 +
Head-fold coven 10 »lh «.miie. Small lailfold
 +
 +
 +
UkcaSS
 +
 +
 +
 +
pleure
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
...
 +
 +
 +
6*ni(i).«tol«llo«0h
 +
 +
 +
 +
 +
Dcrcu ..1 nctvtal lid
 +
 +
UK nulin onRlc d hind Inln unci iruok
 +
 +
 +
 +
 +
CouiriHInii of Islhtnui bMQinint proiwuncnl
 +
 +
 +
byit ol
 +
 +
oprajni
 +
 +
 +
Oik mide^
 +
 +
 +
UkciSS
 +
 +
 +
SmiU epiphyu.
 +
 +
 +
dljtilly
 +
 +
 +
Founb rim. pouch iodi. caled. Cloaiog mem.
 +
 +
Ma """ "■" "^
 +
 +
 +
 +
 +
Three camplete avttic plele
 +
 +
 +
Dudi ol fore and hind
 +
 +
lirea'Sd'l-^
 +
 +
 +
Hcod-fold coven lo iSIb lomlie. Small lall-lold
 +
 +
 +
Alianti^ eiltnding into
 +
 +
 +
 +
 +
 +
 +
 +
 +
jiS
 +
 +
 +
wmm.nttkun
 +
 +
 +
 +
 +
Ccr.l(.L ntiurt a full rlHhi >i>i|lc
 +
 +
 +
 +
 +
MannnMrtcUnDottub.
 +
 +
 +
RdlnilUtet
 +
 +
 +
"'SJS"
 +
 +
X,';.""
 +
 +
 +
Small cpipbiid.
 +
 +
 +
iRd« ai di«n1 tnd.
 +
 +
 +
 +
 +
 +
 +
 +
 +
]/s"
 +
 +
 +
Oval opening inlo»ti.nl' otic ^-ily enendmii
 +
 +
 +
Sameaaja
 +
 +
 +
 +
 +
46
 +
 +
 +
loH
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
oI oUic
 +
 +
 +
 +
Sliiiht deprwlon «I la.
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
from iflih lo lu»t be
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
^"*
 +
 +
 +
 +
 +
10., 1-.
 +
 +
 +
 +
 +
lundlbulutwiun
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
hind nU totnile
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
»»s
 +
 +
 +
I.Tmm.Hd>,uU
 +
 +
 +
 +
 +
fleiure
 +
 +
 +
 +
 +
'=iia'--^'"
 +
 +
 +
Sime u }i
 +
 +
 +
""• " '■
 +
 +
 +
"t'.iors
 +
 +
ollaciory IhanjiS)
 +
 +
 +
Small eplpbiilt
 +
 +
 +
Same a> }i
 +
 +
 +
Same asp
 +
 +
 +
 +
 +
Sime ai yi
 +
 +
 +
Limb bud. i-etun^"
 +
 +
 +
Amniotic umbilicu. •!■ mwi cDiicely do«d
 +
 +
 +
Me»b1a>lolallanu^be. lint U> olend Into Cody cavity
 +
 +
 +
Curving ot 1*11 *nd InCRUC Of cervical Ilea
 +
 +
 +
 +
)l«
 +
 +
 +
us
 +
 +
 +
aurora, BRk'Ull
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
^■""'
 +
 +
 +
Shallow [it
 +
 +
 +
 +
 +
Stmeujr
 +
 +
 +
Sameu]>
 +
 +
 +
 +
 +
Simeaijs
 +
 +
 +
Limb budi
 +
 +
 +
io«idtbolK>"i™H'
 +
 +
 +
Kidt cavlly
 +
 +
 +
Vo nicnni of tall
 +
 +
 +
 +
 +
'"
 +
 +
 +
MS
 +
 +
 +
tj mm. eidi-Ull. t^ mm. (orrmld Inln
 +
 +
 +
 +
 +
 +
 +
 +
 +
doofl? bdialcd
 +
 +
 +
 +
 +
"rjs-r
 +
 +
 +
"ua
 +
 +
 +
like»S
 +
 +
 +
utS^Seprniinn deuly
 +
 +
 +
"i-.r^'sii'-c:
 +
 +
 +
 +
 +
 +
 +
SamcMjaS
 +
 +
 +
 +
 +
Uke ). S
 +
 +
 +
Curving ol lall begun
 +
 +
 +
4S&4&>
 +
 +
 +
'"
 +
 +
 +
 +
 +
 +
 +
 +
 +
limb budl
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
nid dlvenlculum doi. Ing
 +
 +
 +
 +
 +
 +
 +
 +
 +
umiics
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
t» mm Htkiill. >^ mm. l(R-m)d Inln
 +
 +
 +
 +
 +
 +
 +
 +
 +
ckarl) todioiB)
 +
 +
 +
 +
 +
"15"°'
 +
 +
 +
Lalenl
 +
 +
boundUT
 +
 +
 +
VeiT ilijhl dittal W
 +
 +
 +
aunjoiringjojuplure
 +
 +
 +
Oral membrane lunbet
 +
 +
•rluculum "Xed? Tounh i-Uc, pDUcb
 +
 +
 +
 +
 +
 +
 +
aiiiS
 +
 +
 +
Amnion completely cloaed
 +
 +
 +
.*elllaa
 +
 +
 +
Curving ol tall
 +
 +
 +
 +
 +
»a>->i
 +
 +
 +
16 S
 +
 +
 +
' (!« "nnin'*"""'
 +
 +
 +
AWH^n
 +
 +
 +
 +
 +
 +
 +
tm«)j todiuiol
 +
 +
 +
 +
 +
Par.<hac<d
 +
 +
 +
Lalenl
 +
 +
 +
Enginatiun lUchtlr eo
 +
 +
Ruplure ol oral mnn. P«i.tt ipre-oral (ul)
 +
 +
 +
Fourth pouch dearly Ken
 +
 +
 +
 +
 +
 +
 +
"acr
 +
 +
 +
 +
 +
,nlar»cmeoi Into body cavity
 +
 +
 +
 +
 +
"
 +
 +
 +
 +
 +
«s
 +
 +
 +
mm. Ivc-mid tnlo '
 +
 +
 +
 +
 +
 +
 +
 +
 +
cl-tlrlndtaSST'"'
 +
 +
 +
 +
 +
sr
 +
 +
 +
ni U hem Uphoinl
 +
 +
 +
Eniinilion b turon lucknM.diU»lly and jjyb^ .marked ..d»
 +
 +
 +
Sh.Klenin« ol IniiLfina.
 +
 +
lioo ol hvp. oMfii 10 rtifjptn'""' «^ nnil
 +
 +
 +
Oral membrane gone Fourth i-iKcnl puuch
 +
 +
 +
 +
 +
Fouitb aortic arch termed
 +
 +
 +
 +
 +
Cloaed
 +
 +
 +
UUal eolargemeol nol l^iun
 +
 +
 +
Tip of tall begin. 1" U dlrecicd fun>a/da
 +
 +
 +
 +
 +
 +
 +
»s
 +
 +
 +
lA mm. »«k-ull, >«  mm. lonmld Inln
 +
 +
 +
 +
 +
 +
 +
 +
 +
•in*** lodkaiBj
 +
 +
 +
 +
 +
Endol. dun iphniml
 +
 +
 +
like 31
 +
 +
 +
Hemijphcrlcal englna tion
 +
 +
 +
marked
 +
 +
 +
 +
 +
 +
 +
 +
 +
ykejft
 +
 +
 +
Cloaad
 +
 +
 +
gun
 +
 +
 +
 +
 +
Jl*
 +
 +
 +
 +
 +
41 S
 +
 +
 +
M mm. n«kmll, ,,,
 +
 +
 +
Ahoal «6
 +
 +
 +
Same a> 34: Unl hill cf
 +
 +
 +
 +
 +
 +
 +
ESTtS
 +
 +
 +
Deep
 +
 +
 +
 +
 +
Inlundibulam aroadf
 +
 +
 +
Fourth Tbonl poudi
 +
 +
 +
 +
 +
 +
 +
Ailiolbudi
 +
 +
 +
 +
 +
■ holt ilLinlail flaik thaped
 +
 +
 +
 +
 +
 +
 +
01
 +
 +
 +
 +
 +
mm, Ior»nM bnin
 +
 +
 +
 +
 +
bodr lamin* 00 al'lt
 +
 +
 +
 +
 +
 +
 +
f«m>dc&
 +
 +
 +
podTct. tbipcd in
 +
 +
 +
m.arted
 +
 +
 +
fully tBimEil
 +
 +
 +
 +
 +
 +
 +
equal lo
 +
 +
■llDUl i
 +
 +
breidih
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +
68 T
 +
 +
to the apex ol if this measui the age of no] vical flexure ; It is probable the apex of tl classification ( sion may be throughout th been relativel} The follow to the end of ratory courses, to Keibel anc schichte des I 1900. In the of the various It is believed t to enable the the desired sU practically cor the period of d are formed. ' mounts. The work are no tec
 +
 +
Chronoloc
 +
 +
I. Before Layii
 +
 +
1. Maturatic
 +
 +
isthmu;
 +
 +
2. Early cle
 +
 +
the istb membn
 +
 +
3. Later cle^
 +
 +
in the Data for
 +
 +
II. Incubation 1 The period n of the primitive (3) after the app divided by time
 +
 +
 +
 +
{{Ref-Lille1919 TOC}}
 +
{{Footer}}
 +
[[Category:Textbook]][[Category:Chicken]][[Category:Historic Embryology]][[Category:1910's]]

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Lillie FR. The development of the chick. (1919) Henry Holt And Company New York, New York.

Lille 1919: Introduction | Part 1 - 1 The Egg | 2 Development Prior to Laying | 3 Outline of development, orientation, chronology | 4 From Laying to Formation of first somite | 5 Head-fold to twelve somites | 6 From twelve to thirty-six somites | Part 2 - 7 External form of embryo and embryonic membranes | 8 Nervous system | 9 Organs of special sense | 10 Alimentary tract and appendages | 11 The body-cavities, mesenteries and septum transversum | 12 Later development of the vascular system | 13 Urinogenital system | 14 Skeleton | Appendix

Part I The Early Development to the End of the Third Day

Chapter III Outline of Development, Orientation, Chronology

The preceding chapters have traced the development up to the time of laying. The formation of the germ-layers has begun; and the stage of development is fairly definite, though not absolutely constant. When the egg cools, after laying, the development ceases, but is renewed when the temperature is raised to the required degree by incubation.


On the surface of the volk is a whitish disc about 4 mm. in diameter, known as the blastoderm. Edwards gives the average diameter of the unincubated blastoderm (59 eggs) as 4.41 mm., of the area pellucida (50 eggs) as 2.51 mm. The central part of the blastoderm is more transparent and is hence known as the area pellucida; beneath it is the subgerminal cavity. The less transparent periphery is known as the area opaca. In the course of development the embryo, and the embryonic membranes which serve for the protection, respiration, and nutrition of the embryo, arise from the blastoderm.


The embryo proper arises within the area pellucida, which becomes pear-shaped as the embryo forms; the remainder of the blastoderm beyond the embryo is extra-embryonic. From it arise the embryonic membranes known as the amnion, chorion, and yolk-sac. The allantois (Fig. 33 B) arises as an outgrowth from the hind-gut of the embryo, and spreads within the extraembryonic body-cavity; it thus becomes an extra-embryonic membrane secondarily. The growth of the embryo and of the extra-embryonic blastoderm are distinct, though interdependent, processes going on at the same time.


During the first four days of development the blastoderm spreads very rapidly (Figs. 32 and 33). 'Thus on the fourth day (Fig. 33 A) the greater portion of the yolk is already covered. Thereafter the overgrowth of the yolk proceeds much more slowly (cf. Fig. 33 B). In the opaque area there arise, as concentric zones, the area vasculosa distinguished by its blood-vessels and the area vitellina, which may be divided into inner and outer zones (Figs. 32 and 33). The development of the embryo during the same period is indicated in the same figures.



Fig. 32. — A. Hen's egg at about the twenty-sixth hour of incubation, to show the zones of the blastoderm and the orientation of the embryo with reference to the axis of the shell. (After Duval.) B. Yolk of hen's egg incubated about 50 hours to show the extent of overgrowth of the blastoderm. (After Duval.)

A. C, Air chamber, a. p., Area pellucida. a. v., Area vasculosa. a. v. e., Area vitellina externa, a. v. i., Area vitellina interna. Y., Uncovered portion of yolk.


The blastoderm early becomes divided in two layers as far as the margin of the vascular area. The outer layer, known as the somatopleure, is continuous with the body-wall, which is open ventrally in the young embryo. The inner one, known as the splanchnopleure, is continuous with the wall of the intestine which is likewise open ventrally. The space between these two membranes, the extra-embryonic body-cavity, is continuous with the body-cavity of the embryo. Ultimately, the splitting of the blastoderm is carried around the entire yolk, so that the latter is enclosed in a separate sac of the splanchnopleure, the yolk-sac, which is connected by a stalk, the yolk-stalk, to the intestine of the embryo. This stalk runs through an opening in the ventral body-wall, the umbilicus, where the amnion, which has developed from the extra-embryonic somatopleure, joins the body-wall (Fig. 33 B).


About the nineteenth day of incubation the yolk-sac is drawn into the body-cavity through the umbiUcus, which thereupon closes. The young chick usually hatches on the twenty-first day. Orientation. It is an interesting and important fact that the embryo appears in a definite relation to the line drawn through the axis of the entire egg, or to the line joining the bases of the two chalazse, which is usually the same thing. If the egg be placed as in Fig. 32 A, with the blunt end to the left, the head of the embryo will be found directed away from the observer when the blastoderm is above; the left side of the embryo is therefore towards the broad end, and the right side towards the narrow end of the egg. According to Duval this orientation is found in about 98.5% of eggs: of 166 eggs observed, in which the embryo was formed, Duval found 124 oriented exactly in this manner, 39 in which the axis of the embryo was slightly oblique, 2 in which the head was towards the broad end, and 1 in which the usual position was completely inverted. In the pigeon's egg the orientation of the embryo is equally definite, but slightly different. The axis of the embryo cuts the axis of the entire egg at an angle of about 45°, the head of the embryo being directed away from the observer to the right, when the broad end of the egg is to the observer's left as in Fig. 32 A.



Fig. 33. — A. Yolk of hen's egg incubated 84 hours. (After Duval.) B. Embryo and membranes of the hen's egg on the seventh day of incubation. (After Duval.)

AL, AUantois. Am., Amnion, a. v., (in B) Area vitellina. E., Embryo. S. t., Sinus terminalis. Other Abbreviations as in Fig. 32.


The definiteness of orientation of the embryo with reference to the axis of the egg enables one to distinguish anterior and posterior ends of the blastoderm before there is any trace of an embryo; and while there is no possibility of orientation by examination of the blastoderm itself, or when such orientation is otherwise extremely difficult. By the method of orienting the blastoderm w^ith reference to the axis of the shell, observers have been able to discover important features of the early development which would otherwise, no doubt, have escaped observation The relation is of interest in other respects discussed in their appropriate places. (See p. 15.)

Chronology (Classification of Stages)

The development of an animal is an absolutely continuous process, but for purposes of description it is necessary to fix certain stages for comparison with those that precede and those that follow. Each stage has a certain position in the continuous process, and the correct arrangement of stages is therefore a sine qua non for their correct interpretation. This may seem a very simple matter seeing that development is in general from the more simple to the more complex. And it would be so if it were not for the fact that embryonic stages, like the adult individuals of a species, vary more or less, so that no one embryo is ever exactly like another. These embryonic variations involve (1) the rate of development of the whole embryo, so that at a given time in the process no two embryos are in exactly the same stage; (2) the relative rates of development of different organs; (3) the size of the embryo, for embryos of the same stage of development may vary somewhat in size.


Although the total period of incubation is fairly constant in the hen's egg, about twenty-one days, yet there is great variation in the grade of development of embryos of the same age, especially during the first week. This is due to two main factors: first, variation in the latent period, that is the time necessar}^ to start the development of the cooled blastoderm after the egg is put into the incubator, and second, to variation in the temperature of incubation. Individual eggs may vary in rate of development when these two factors are constant, but this difference is relatively slight. Other things being equal, the latent period varies with the freshness of the egg; it is relatively short in eggs that are newly laid, and long in eggs that have remained quiescent some time after laying. It is obvious that the latent period will form a more considerable portion of the entire time of incubation in early than in late stages. Hence the difficulty of classifying embryos, particularly in the first four or five days of incubation, by period of incubation. Eggs procured from dealers usually show such great variations in degree of development, at the same time of incubation, that it is quite impossible to grade them with any high degree of accuracy by time of incubation. It is statf'd also that the rate of development varies considerably at different seasons, other factors being constant. But this has not been found to be a serious matter in my own experience.


Variations in temperature, either above or below the normal, also seriously affect the rate of development, and produce abnormalities when extreme. If the temperature be too low, the rate is slower than normal; if too high, the rate increases up to a certain point, beyond which the egg is killed.


The physiological zero, that is the temperature below which the blastoderm undergoes no development whatever, has been estimated differently by different authors. Some place it at about 28° C, others at about 25°; Edwards places it as low as 20-21° C. At the last temperature, apparently, a small percentage of eggs will develop in the course of several days to an early stage of the primitive streak, but most eggs show no perceptible development. In very warm weather, therefore, the atmospheric temperature m.ay be sufficient to start eggs. The following table is given by Davenport based on Fere's work:

Temperature .34° 35° 36° 37° 38° 39° 40° 41°

Index of Development 0.65 0.80 0.72 1.00 1.06 1.25 1.51

The index of development represents the proportion that the average development at a given temperature in a given time bears to the normal development {i.e., development at the normal temperature for the same time). There is an increase in the rate up to 41°; a maximum temperature, which cannot be much above 41°, causes the condition of heat-rigor and death.

There would seem to be no better way to determine the normal temperature for incubation than by measuring the temperature of eggs incubated by the hen throughout the entire period of incubation. This has been done very carefully by Eyclesh3mier, who finds the internal temperature of such eggs to be as follows:


Day of incubation


1


2


3


4


5


Temperature of hen


102.2


103.0


103.5


104.0


103.8


Temperature of egg


98.0


100.2


100.5


100.5


100.4


Day of incubation


6


7


8


9


10


Temperature of hen


105.0


104.6


104.5


105.0


105.0


Temperature of egg


101.0


101.8


102.5


101.6


102.0


Day of incubation


11


12


13


14


15


Temperature of hen


104.8


105.2


104.5


105.0


105.2


Temperature of egg


101.8


102.2


102.0


102.5


102.0


Day of incubation


16


17


18


19


20


Temperature of hen


105.0


104.6


104.8


104.5


104.5


Temperature of egg 103.0 102.4 103.0 103.0 103.0

The temperature of the hen is seen to be somewhat higher than that of the eggs. In an artificial incubator where 85 % of the fertile eggs hatched on the twentieth and twenty-first da3^s, the temperatures were as follows:

Day of incubation Temperature of incubator Temperature of egg

Day of incubation Temperature of incubator Temperature of egg

Day of incubation Temperature of incubator Temperature of egg

Day of incubation Temperature of incubator Temperature of egg

It would be possible then to establish a normal rate of development, by using perfectly fresh eggs incubated at a normal temperature. In practice I have found that the times given in Duval's atlas are approximately normal, and these are, therefore, adopted so far as given. But even under the best conditions the variations are sufficient to prevent close grading of stages by time of incubation in the first three days. This may be due to differences in the grade of development at the time of laying, owing to varia


1


2


3


4


5


102.0


102.0


103.0


102.0


102.5


99.5


100.0


101.0


100.5


100.5


6


7


8


9


10


103.0


102. 5


102.0


103.0


103.5


101.0


100.0


100.0


101.0


101.5


11


12


13


14


15


103.0


103.5


104.0


103.5


104.0


101.5


101.8


102.0


102.5


103.0


16


17


18


19


20


104.5


104.0


103.5


104.0


104.5


103.0


103.0


102.5


102.5


103.5


tioRS in the time of development in the oviduct and uterus, or to slow development before incubation in warm weather, or to individual variation. It becomes necessary, therefore, to find some other system. The method followed by a considerable number of investigators, namely to classify by the number of somites, has been found to be best between about the twentieth and ninetv-sixth hours of incubation. In the table which follows, therefore, this method of classification is used. For the sake of brevity throughout the book a stage reckoned by the number of somites will be w^ritten 1 s, 2 s, 3 s, etc. It is true that the relative rate of the development of organs varies slightly. Nevertheless, classification by number of somites is unquestionably the most exact method up to the end of the fourth day at least. Beyond this stage the method is difficult to apply, and after about the sixth day the number of somites becomes constant. After the fourth day the time of incubation is usually a sufficiently exact criterion for most purposes: the latent period has become a relatively inconsiderable fraction of the whole time of incubation, and the embryos that survive, assuming fresh eggs and normal temperature of incubation, are in about the same stage of development.


Classification of embryos by length is a favorite method particularly in Germany, and it offers many advantages in the case of some animals; under many conditions it is the only available method. But it offers considerable difficulties, the most serious of which come from the varying degrees of curvature of the embryo. In early stages of the chick, for instance, up to about 12 s, the total length of the embryonic axis may be measured, for the embryo is approximately straight. The cranial flexure then begins to appear, and slowly increases to a right angle; during this period there may be an actual reduction in length of the embryo (cf. table, 14-16 s). Conditions are also complicated by the fact that the head of the embryo is turning on its left side at the same time. The cervical flexure then appears and causes a second reduction of the total length (cf. table 2932 s). Later still the curvature of the trunk and particularly of the tail develops in somewhat varying degrees and makes bad matters worse. After these flexures are formed, let us say at about eighty hours in the chick, it is customary to take the so-called neck-tail measurement, that is, from the cervical flexure to the apex of the tail flexure. But even then it is questionable if this measurement is as accurate a means of classification as the age of normally incubated embryos; particularly as the cervical flexure is secondarily eliminated by raising of the head. It is probable that the measurement from the tip of the head to the apex of the cranial flexure (head-length) would be best for classification of chick-embryos by measurement. This dimension may be readily taken, after the cranial flexure begins, throughout the entire period of incubation. However, it has been relatively little used up to the present time.


The following tables give the chronology of development up to the end of the fourth day, the period usually covered in laboratory courses. For the later chronology the student is referred to Keibel and Abraham's Normaltafeln zur Entwickelungsgeschichte des Huhnes (Gallus domesticus), Jena, Gustav Fischer, 1900. In the various chapters of Part II, the later chronology of the various organs is given here and there throughout the text. It is believed that these references will be sufficient on the Avhole to enable the student to determine what embryos to select for the desired stage of most organs. The tables have been made practically continuous from 1 s up to 41s, because these cover the period of development in which the primordia of most organs are formed. They have been constructed mostly from entire mounts. The corresponding tables in Keibel and Abraham's work are noted by number in the right-hand column.

Chronological Tables of the Development of the Chick

I. Before Laying:

1. Maturation and fertilization; found in the oviduct above the isthmus.

2. Early cleavage up to about the thirty-two celled stage found in the isthmus of the oviduct during the formation of the shellmembrane (Patterson) .

3. Later cleavage, formation of periblast and entoderm, etc., found in the uterus up to time of laying. Data for the pigeon given in Chapter II; see legends to figures.

II. Incubation to Formation of the First Somite:

The period may be divided in three parts: (1) before the appearance of the primitive streak; (2) primitive streak formed but no head process; (3) after the appearance of the head-process. These stages may be subdivided by time or by length of the primitive streak.














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Fuilon of Ul. haira of bean incomplete


Bel-een . ind 18







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Henri bent lUghlly lo right

He.in bent lo right






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urc-gul doMd 1.4 mm.



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leadfold coven nlremc




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tip ol head











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180 10 go


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9 mm. pealBI Imgih



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Lenmb ol loregul 1 1 mm. Two iiKenJ (utnin. .liU closed



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lead fold conn anlerior

put of hind brain



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4 houn IUuvbI)


udrullyluniBllaltli. Cnnlul and iin-icol ncnira rouodri ob



'"Sa


Sllfhl nar = s

deep pit




Na indioillDa ol hypopbi-ai


.luough



\unculo i-enlricubir Ditunnndicaiedbyoon.



Like 18 S




'*


OS


..s


1„7.ES.»



.elLlumrdloBlhlDmllt Cr.ni.1 (tuure-riibi anilt.itf.neiujmr)

Only In lail


^j^!J!^bJr


"sill'


olpi.




Hypophi-iii barely InHi

ihrouKh

jd Yi*. pouch Kcn



I'tnliiculai loop noir vcnlnl ID »ur.-«n.



™"""""



Sudden venlrally lumed neiure ol trunk .boui 8th wmiie (due 10


»*-3J


»»


...


""


.ifllurncdloi-flinmlle. Cr.oljinau«al"UI* r. anilc. Mr., (tuui.

vm .fi»hi


S'U


«IM«»S


»^™j, sr


Ukt 11 S




like 11 S


Lenglh ol lore-gut t-J mm.olhcmiKJikeiiS



Uke >i S



tleadlold CTOHO id ni ani pouch nod id « 




'a

J6»


fjS


J, T mm, gntUM fcnph



jrviol nciun >nitc nl


D uil bud


Uk. a.S



Moulholpil




vi^naliaa In ftoDI Dl


Lenglh ol lore-gut 1 ij

«S'riy"pertaraie4"m



Like 31 S,



■Jead-fnld covem lo lolh



Tail. fold barely indlcaled


iS-.i»


J6j













iraoj



oral plate


upper angle
















■iiuuled
















<i.i mm, (TtaloJ kniib



.crriol nenire lite ijS.


n tail bud



Iduiniai


Rebii«ly



nalioninNo.jSi(liSl


"^^^pllTfl^,"^^


Lenilh nl lute-gul about



Apei of i-Hilriclc vcnlnl



^"t!^"™""**



NolaU-fold


'


M-»» S


iitlan> n[ tnin mnrc






U^n™. n«hl "^k




iliUopcn


oponingol SUml"'^




lion in (funl ol oral pbU




Two complete aoftlc arches








.. s


6*«™.p«i«.i«.rh


a houn


di^.l',"™cl ""


■> tall bud


llkc«-.jS


louth. ol


yke.4-.1S



\o epiphnii


Same ai 14-aJ S


»mc a. 14-1; S



Sam.aa«-.^S. ^^^^ archB-^fl^d?*"""



rtndlold cover. 10 171b



Tall-fold indicaled



049



,™n.,g™,«nr«„h


9 houn


epiuilk fluura •llihlly ICB Ihan ixHCcUni


nun bud



toulh ol




No cpipbtiii


"E?^ '-'"■!


d ri«*ral pouch ndl deielo[cd. Thyroid and lung divauoili



Two complelE aortic arehu- Third nearly



lead-fold coven to >otl> lomite



Tail bud projecu behind Hlnd-gul lorma n bay



Ji8








"So"




Hcll muked

















H^^o




















icf














a , mm palru Imilh



"crvlcal Ituurt man




Mouih ol


OHe KBcIe


rUckenlns


Epiph,Ti. , iMTTU >liRht


Same as ,7 S


'.aztir.sii-


rhicT complete aortic



FalJ-fold formed . con

Form. <maU side o|in



4j


4'








'p^cillSf,


•Imuil


0( MIO dem. No





uilhn



11°^ fX'" "u^


pouch











diaed



tn"^""








»mite"""







-., mm. nW" """



UVe i« S




Like iB S


Like » S


UkcittS


No cplpb^Ul


Same M ay


JkeiH. Oml membrane



Thn» complele aortic arcbci


Bud3olhlnd limba Indialed by thickening


Head-fold coven 10 »lh «.miie. Small lailfold


UkcaSS


pleure







...


6*ni(i).«tol«llo«0h



Dcrcu ..1 nctvtal lid

UK nulin onRlc d hind Inln unci iruok



CouiriHInii of Islhtnui bMQinint proiwuncnl


byit ol

oprajni


Oik mide^


UkciSS


SmiU epiphyu.


dljtilly


Founb rim. pouch iodi. caled. Cloaiog mem.

Ma """ "■" "^



Three camplete avttic plele


Dudi ol fore and hind

lirea'Sd'l-^


Hcod-fold coven lo iSIb lomlie. Small lall-lold


Alianti^ eiltnding into





jiS


wmm.nttkun



Ccr.l(.L ntiurt a full rlHhi >i>i|lc



MannnMrtcUnDottub.


RdlnilUtet


"'SJS"

X,';.""


Small cpipbiid.


iRd« ai di«n1 tnd.





]/s"


Oval opening inlo»ti.nl' otic ^-ily enendmii


Sameaaja



46


loH









oI oUic


Sliiiht deprwlon «I la.






from iflih lo lu»t be











^"*



10., 1-.



lundlbulutwiun






hind nU totnile






»»s


I.Tmm.Hd>,uU



fleiure



'=iia'--^'"


Sime u }i


""• " '■


"t'.iors

ollaciory IhanjiS)


Small eplpbiilt


Same a> }i


Same asp



Sime ai yi


Limb bud. i-etun^"


Amniotic umbilicu. •!■ mwi cDiicely do«d


Me»b1a>lolallanu^be. lint U> olend Into Cody cavity


Curving ot 1*11 *nd InCRUC Of cervical Ilea


)l« 


us


aurora, BRk'Ull







^■""'


Shallow [it



Stmeujr


Sameu]>



Simeaijs


Limb budi


io«idtbolK>"i™H'


Kidt cavlly


Vo nicnni of tall



'"


MS


tj mm. eidi-Ull. t^ mm. (orrmld Inln





doofl? bdialcd



"rjs-r


"ua


like»S


utS^Seprniinn deuly


"i-.r^'sii'-c:




SamcMjaS



Uke ). S


Curving ol lall begun


4S&4&>


'"





limb budl








nid dlvenlculum doi. Ing





umiics







t» mm Htkiill. >^ mm. l(R-m)d Inln





ckarl) todioiB)



"15"°'


Lalenl

boundUT


VeiT ilijhl dittal W


aunjoiringjojuplure


Oral membrane lunbet

•rluculum "Xed? Tounh i-Uc, pDUcb




aiiiS


Amnion completely cloaed


.*elllaa


Curving ol tall



»a>->i


16 S


' (!« "nnin'*"""'


AWH^n




tm«)j todiuiol



Par.<hac<d


Lalenl


Enginatiun lUchtlr eo

Ruplure ol oral mnn. P«i.tt ipre-oral (ul)


Fourth pouch dearly Ken




"acr



,nlar»cmeoi Into body cavity



"



«s


mm. Ivc-mid tnlo '





cl-tlrlndtaSST'"'



sr


ni U hem Uphoinl


Eniinilion b turon lucknM.diU»lly and jjyb^ .marked ..d»


Sh.Klenin« ol IniiLfina.

lioo ol hvp. oMfii 10 rtifjptn'""' «^ nnil


Oral membrane gone Fourth i-iKcnl puuch



Fouitb aortic arch termed



Cloaed


UUal eolargemeol nol l^iun


Tip of tall begin. 1" U dlrecicd fun>a/da




»s


lA mm. »«k-ull, >«  mm. lonmld Inln





•in*** lodkaiBj



Endol. dun iphniml


like 31


Hemijphcrlcal englna tion


marked





ykejft


Cloaad


gun



Jl*



41 S


M mm. n«kmll, ,,,


Ahoal «6


Same a> 34: Unl hill cf




ESTtS


Deep



Inlundibulam aroadf


Fourth Tbonl poudi




Ailiolbudi



■ holt ilLinlail flaik thaped




01



mm, Ior»nM bnin



bodr lamin* 00 al'lt




f«m>dc&


podTct. tbipcd in


m.arted


fully tBimEil




equal lo

■llDUl i

breidih






68 T

to the apex ol if this measui the age of no] vical flexure ; It is probable the apex of tl classification ( sion may be throughout th been relativel} The follow to the end of ratory courses, to Keibel anc schichte des I 1900. In the of the various It is believed t to enable the the desired sU practically cor the period of d are formed. ' mounts. The work are no tec

Chronoloc

I. Before Layii

1. Maturatic

isthmu;

2. Early cle

the istb membn

3. Later cle^

in the Data for

II. Incubation 1 The period n of the primitive (3) after the app divided by time


Lille 1919: Introduction | Part 1 - 1 The Egg | 2 Development Prior to Laying | 3 Outline of development, orientation, chronology | 4 From Laying to Formation of first somite | 5 Head-fold to twelve somites | 6 From twelve to thirty-six somites | Part 2 - 7 External form of embryo and embryonic membranes | 8 Nervous system | 9 Organs of special sense | 10 Alimentary tract and appendages | 11 The body-cavities, mesenteries and septum transversum | 12 Later development of the vascular system | 13 Urinogenital system | 14 Skeleton | Appendix

Cite this page: Hill, M.A. (2019, December 9) Embryology Book - The development of the chick (1919) 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_development_of_the_chick_(1919)_3

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G