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XX. The Interdependence of the Various Developmental Processes

By Franz Keibel. Freiburg i. Br.

Except in the chapters in which the earlier stages of development are considered and in that in which a review of the entire development and of the elaboration of the external form is given, the development of the various organs and systems of organs has been so far presented as if it took place for the most part individually and independently for each organ or system. We have now to consider how the development of the individual organs combines to produce the development of the whole. It is clear that the normal fully developed organism cannot be produced without a certain regular succession in the development of the organs and a regular interdependence of the individual developmental processes, but it is open to question whether this interdependence is the result of the individual and independent development of each organ taking place in such a way that it fits into that of the others or whether it is due to the individual anlagen of an organism mutually influencing one another during development so as to cause the formation of a normal organism. Both these views have their supporters. Roux (1893) advocates the theory that the various cell complexes of the ovum differentiate independently even from the segmentation stages (Mosaictheory).


Mehnert (1895) says: " The study of the individual time differences in the differentiation of the same organ within the same species shows that a constant correlation of the organ development in the same embryo does not exist." " The frequently striking lack of correlation in the development of organs shows that each developmental process in an organ is to a certain extent an independent process. The development of a vertebrate embryo consists of a series of successive individual processes, regulated only by phylogenetic relations. Only the form and position of any organ can be modified by the environment, ' : Also, so worthy and thoughtful an observer as Born (1897), in his investigations in regeneration in Amphibian larvae, comes to the conclusion that the development from its beginning (that is to say, from larvae in which the medullary canal had just closed and the tail-bud had begun to grow out) 1 depends essentially on the self -differentiation of the individual parts. ' ' A correlation influence of the neighboring parts or of the whole caD never be perceived — neither a negative nor a positive one. ,; " The development corresponds throughout to the mosaic theory of Roux." On the other hand, His has incorrectly been claimed as an advocate of this view. He says (1874) in the sixteenth letter of " Unsere Korperform": "The orderly connection of all the processes underlying the development of the body is a principle which the theory of descent must take into consideration in the future to a greater extent than it has up to the present. So long as investigators of phylogenetic problems have been content to sketch out special histories of individual organs or parts of organs, so long have they perceived the task to be accomplished only in what is certainly a very limited portion of its actual extent; for the development of each individual organ is always merely a dependent partial phenomenon of a huge total process, which links itself up in all directions.' 1 He expresses himself similarly in his paper on " Die Entwicklung der menschlichen und tierischen Physiognomien " (1892), and in his treatise on "Der Prinzip der organbildenden Keimbezirke und die Verwandtschaften der Gewebe " (1901) he assumes the existence not only of spatial and temporal but also of chemical influences ; consequently the principle of " organ forming germinal areas " that His has established is not to be interpreted in the sense of Roux's mosaic theory.


A standpoint similar to that of His is also taken by 0. Hertwig. In various places in his writings he maintains that all the individual parts of the embryo always develop in relation to one another and the development of each part is dependent on the development of the whole (compare 0. Hertwig, 1892 and 1906). This is the view that I also hold, and in what follows I shall endeavor to supply further reasons in support of it. I am of the opinion that the individual anlagen of an organism mutually influence one another in the development so as to contribute to the production of a normal organism. I do not in this dispute the fact that a relatively great individuality, varying in amount in different species of animals, occurs in the development of individual organs and organ complexes. That this is so is shown by the investigations of Born, already referred to, and also by numerous malformations, of man as well as of other animals; in these, individual organs or parts of organs may be developed relatively normally, while others may be abnormal to a high degree or may even be wanting. But neither by the experiments of Born and others, among which those of W. H. Lewis (1907) may be especially mentioned, nor yet by such malformations is it disproved that the individual developmental processes influence one another.


  • 1 For earlier stages there are similar investigations by W. H. Lewis, who transplanted pieces of the dorsal and lateral lip of the blastopore of Bana palustria and was able to show that even the different parts of the blastopore lip possessed in a high degree the power of self-differentiation.


Fischel (1896) has been led to assume such an influence from the measurements he has made of duck embryos with from 1 to 20 primitive segments. He finds that the older the embryo the more regular is the relation of the individual portions of the body one to another, and assumes that during the development regulating influences make themselves felt and bring it about that gradually a distinctly orderly structure of the body supervenes, whereby variations become slighter and rarer." He regards the correlation of the developing organs as such a regulating influence. It may be remarked that long ago Karl Ernst von Baer (1828) arrived at similar conclusions. Furthermore, one may appeal to experimental observations for evidence of the existence of a correlation between the individual parts of a developing ovum, as, for instance, the fundamental experiments in which several embryos are obtained from a single ovum, the experiments of Lewis (1904) and Spemann (1901, 1903) on the relation of the development of the lens to the optic cup and numerous experiments in regeneration.


In many of these experiments one may imagine a pure contact action, in others one must assume action at a distance. Undoubtedly action at a distance obtains when the development is influenced by the reproductive gland. I do not intend to enter into details here as to the effects of castration, but will merely recall the influence that it has unquestionably been shown to exert on the formation and growth of the bones. The epiphyses persist for a longer time and so the growth also lasts longer (compare Sellheim, 1899). Very interesting for their bearings on the doctrine of action at a distance in development are the investigations of Paton and Goodall (1904) and Paton (1904) on guineaKins, and especially those of Hammar (1909) and his pupils, Soederlund and Backman (1909), Jonson (1909) and Syk (1909) on the development of the thymus in the rabbit and man. The human thymus and also that of the mammalia grows until the onset of sexual maturity and then undergoes a rapid involution. Also the occurrence of an age-involution of the lymphoid tissue (Berry and Lack, 1906) may be mentioned. Furthermore, Hammar's pupil Lindberg has found that at about the time of puberty the number of the blood lymphocytes distinctly diminishes. To what extent the suprarenal bodies, as well as the functioning reproductive glands, inhibit a development of the thymus, acting as thymus depressors, and to what extent the thyreoid, the hypophysis, and the parathyreoids favor it, acting as thymus excitators, will not be further considered here. These are investigations that have invaded new territories and still need much enlargement.


The investigation of the interdependence of the various developmental processes has been the purpose of the publication by Keibel (since 1897) of the Normentafel zur Entwicklungsgeschichte der Wirbeltiere. A Normentafel zur Entwicklungsgeschichte des Menschen has been published by Keibel and Elze (1908) and some of the tables given in this may find place here.


Insert formatted table here


Human Embryo Pfannenstiel “Klb
Kroemer-Pfannenstiel. Collection of Prof. Pfannenstiel, Giessen. Carnegie stage 10
Desig. Size Age Body form Primitive streak Primitive segments Chorda Nervous system Eye Ear Nose Hypophysis Mouth Digestive trac, liver and pancreas Branchial pouches, threoid thymus, trachea and lungs Urogenital system Heart and vessels Integument Skeleton Extremities Amnion Allantois Remarks
3 Human embryo Klb. N.T. Fig. 3a and 3d; Text-fig 5a to 5n. 138 sections of 10 μ = 1.38 mm. The age is estimated by Born at from 10 to 14 days. No dorsal bend. Head end bent down at right angles and cut by 24 sections of 10 μ. Still indications of a neurenteric canal. Short primitive streak. CIoacal membrane. 5-6 pairs of primitive segments. The chorda throughout is contained in the entoderm. The medullary canal is everywhere wide open, but the brain portion is aire ady marked off from the cord and shows beginning segmentation. Optic anlage not yet evident. Primary pharyngeal membrane No oral sinus. The 1st branchial pouch is formed but does not reach the ectoderm. Heart ventral, but still paired. Paired aortse. 1st branchial arch artery. Aa. umbilicales. Yv. omphalo-mesentericae. Vessels on the yolk sack full of blood corpuscles. No amniotic duct evident. Allantoic duct Obtained by laparotomy.
Size

Kroemer gives the following data: "The greatest length of the embryonic anlage from the anterior edge of the amnion of the head cap to the chorion end of the belly-stalk 1.95 mm, the length of the embryo without the belly-stalk from the head to the tail 1.8 mm., the greatest width of the yolk sack barely 1.2 mm, the width of the embryonic disk at the boundary between the amnion and yolk sack (measured in the head view) 0.9 mm. The measurements of the yolk sack were 1.1 mm, (height), 1.4 mm (width), 1.5 mm. (length)."

Remarks

Fixation: Mailer's fluid. Stain: alum carmine; paraffin. Sections: 10 micron Transverse

Literature: Pfannenstiel in Handbuch der Geburtshilfe, published by Winckel, Wiesbaden 1903. — Kroemer, Wachsmodell eines jungen menschl. Embryo. Verhandl. d. Ges. f. Gynakologie, 1903. The wide pericardial cavity is not connected with the peripheral ccelom. The embryonic ccelom is being formed caudally. On the chorion the layer of Langhans cells and syncytium.

Reference: Keibel F. and Elze C. Normal Plates of the Development of the Human Embryo (Homo sapiens). (1908) Vol. 8 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.
Cited in: 1912 Human Embryology
1908 Embryo Tables: Klb (stage 10) | Pfannenstiel III (stage 11) | Meyer 300 (stage 12) | Strahl 4mm (stage 13) | Hertwig G31 (stage 14)
Human Embryo Pfannenstiel III
Collection of Prof. Pfannenstiel, Giessen. Carnegie stage 11
Desig. Size Age Body form Primitive streak Primitive segments Chorda Nervous system Eye Ear Nose Hypophysis Mouth Digestive trac, liver and pancreas Branchial pouches, threoid thymus, trachea and lungs Urogenital system Heart and vessels Integument Skeleton Extremities Amnion Allantois Remarks
6 Pfannenstiel III Fig. Vr and Vv. Textfig. 6a to 6w. Gr. L. about 2.6 mm. Embryo bent over the ventral surface and slightly bent spirally. Tail bud, on its ventral side doubtful remains of primitive streak. 13-14 pairs of primitive segments. Chorda emerging from entoderm, Cranially is still entoderm, caudally it is probably primarily independent of the entoderm and in this region it is no longer included in the entoderm. In brain region medullary canal is open to caudal to the region of the optic vesicle, similarly the caudal end. Anlagen of neuromeres already present. Primary optic vesicles. They are close to the ectoderm; in their region the medullary canal is wide open. Anlage of auditory vesicle recognizable as a thickened and at first but little depressed plate of ectoderm. Hypophysis just indicated. Primary pharyngeal membrane still closed. Oral sinus. Wide hepatic bay just cranial to the intestinal umbilicus. No trace yet of hepatic trabeculae. The two first branchial pouches reach the ectoderm, the 3rd is formed. Quite rudimentary "pronephric anlage" in 8th, 9th and 10 pairs of primitive segments. No trace yet of a Wolffian duct. Segmental vesicles in the 11th, 12th and 13th pairs of primitive segments. Heart S-shaped. Posterior mesocardium through a few sections. Aorta paired throughout. Allantoic duct Extirpation of uterus on account of carcinoma.
Remarks - Fixation formalin Muller's fluid. Stain Paracarmine. Sections 10 μ. Recent mitoses. Septum transverse. No ventral connection between pericardial and peritoneal cavities.
Reference: Keibel F. and Elze C. Normal Plates of the Development of the Human Embryo (Homo sapiens). (1908) Vol. 8 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.
Cited in: 1912 Human Embryology and

Low A. Description of a human embryo of 13-14 mesodermic somites. (1908) J Anat Physiol. 42(3): 237-51. PMID 17232769 | PMC1289161

1908 Embryo Tables: Klb (stage 10) | Pfannenstiel III (stage 11) | Meyer 300 (stage 12) | Strahl 4mm (stage 13) | Hertwig G31 (stage 14)
Human Embryo No. 300
Collection of Professor R. Meyer, Berlin. Carnegie stage 12
Desig. Size Age Body form Primitive streak Primitive segments Chorda Nervous system Eye Ear Nose Hypophysis Mouth Digestive trac, liver and pancreas Branchial pouches, threoid thymus, trachea and lungs Urogenital system Heart and vessels Integument Skeleton Extremities Amnion Allantois Remarks
7
N.T. Fig. VI 1, VI r ind VI v.
Gr. L. 2.5 mm. Remains of primitive streak. Cloacal membrane. 23 pairs of primitive segments. Chorda separated from entoderm, Anterior neuropore closed. but its position still recognizable. Medullary canal stili wide open for a stretch caudally. Roof of 4th vent, beginning to thin out. Neuromeres. Trigeminus and acustico-facialis ganglia distinct. Optic vesicles. Mesoderm between ectoderm and optic vesicle, Auditory vesicle almost closed (open through 4 or 5 sections of 5μ). Ductus endolymphaticus not yet visible. Anlage doubtful. Pharyngeal membrane just torn, still abundant remains of it. Intestine still communicates widely with the yolk sack. Liver a thick-walled sack from which the trabeculse are beginning to bud. The 3 anterior branchial pouches reacts the ectoderm; the 4th, though formed, does not. Thyreoidea mediana formed. Pulmotracheal groove. The paired condition of the pulmonary anlage already indicated. Rudimentary "pronephric anlage" Heart S-shaped. Allantoic duct The embryo was obtained by operation.
Remarks

Abundant mitoses in the embryo. Fixation: ? Stain: Borax carmine. Sections: 5 μ. The embryo was modelled by Dr. Peter Thompson (1907) Also see Meyer (1904)

Reference: Keibel F. and Elze C. Normal Plates of the Development of the Human Embryo (Homo sapiens). (1908) Vol. 8 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.
Cited in: 1912 Human Embryology and

Thompson P. Description of a human embryo of twenty-three paired somites. (1907) J Anat Physiol, 41(3):159-71. PMID 17232726; Meyer, Rob., Ueber die Beziehung der Umierenkanalchen zum Coelomepithel, etc., Anat. Anz., Vol. 25, 1904

1908 Embryo Tables: Klb (stage 10) | Pfannenstiel III (stage 11) | Meyer 300 (stage 12) | Strahl 4mm (stage 13) | Hertwig G31 (stage 14)
Human Embryo 4 mm
Collection of Prof. Strahl, Giessen. Carnegie stage 13
Desig. Size Age Body form Primitive streak Primitive segments Chorda Nervous system Eye Ear Nose Hypophysis Mouth Digestive trac, liver and pancreas Branchial pouches, threoid thymus, trachea and lungs Urogenital system Heart and vessels Integument Skeleton Extremities Amnion Allantois Remarks
7
N.T. Text-fig 9a-9s.
Gr. L. 4 mm. Between Figs. 5 and 7 of His" Normenta- fel. (The embryo of Fig. 6 of His' Nor- mentafel is probably pathological.) Vertex bend complete. Nape bend has begun. Chorda separated from entoderm, but in the cranial part, through 19 sections, it has as yet no mesoderm below it. Optic vesicles. Mesoderm between ectoderm and optic vesicle,
Remarks -
Reference: Keibel F. and Elze C. Normal Plates of the Development of the Human Embryo (Homo sapiens). (1908) Vol. 8 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.
Cited in: 1912 Human Embryology
1908 Embryo Tables: Klb (stage 10) | Pfannenstiel III (stage 11) | Meyer 300 (stage 12) | Strahl 4mm (stage 13) | Hertwig G31 (stage 14)
Human Embryo G31
Collection of Prof. O. Hertwig, Anat-biol. Institute, Berlin.Carnegie stage 14
Desig. Size Age Body form Primitive streak Primitive segments Chorda Nervous system Eye Ear Nose Hypophysis Mouth Digestive trac, liver and pancreas Branchial pouches, threoid thymus, trachea and lungs Urogenital system Heart and vessels Integument Skeleton Extremities Amnion Allantois Remarks
14 Human embryo G 31. N.T. Fig. VIII. Text-fig. 12a-12p. Gr. L. = nape-breech length, 4.9 mm. vertex-breech length 4.7 mm. Greatest diameter of yolk sack 0.58 mm Supposed to be 4 weeks. Between Figs. 6 and 7 of His' Normentafel, nearer Fig. 7. Vanished up to the tail bud. 35 pairs of primitive segments, the most anterior quite rudimentary. The anterior end terminates close to the hypophysis. Very thin chord sheath. Infundibulum. Roof of the 4th ventricle thin. 7 distinct neuromeres in 4th ventricle region. No dorsal columns in spinal cord as yet. Neuroenteric cord. Transition from optic vesicle to otic cup. Lens represented by thickened area of ectoderm,. Scattered mesenchyme cells between lens and otic vesicle. Auditory vesicle just constricted off. The point of constriction still visible at the ectoderm. Ductus endolymphaticus just formed. Distinct convex olfactory areas. Very broad hypophyseal pouch. No remains of pharyngeal membrane. Tuberculum impar. Stomach anlage already slightly twisted. Tail gut. Abundant trabeculae in liver anlage. Gall-bladder formed. Distinct anlage of dorsal pancreas. Early anlage of ventral pancreas. (Jankelowitz 1895 describes 2 ventral pancreas anlagen. Itis doubtful if there are really two; it seemed to us that there was only one.) 4 branchial pouches reach the ectoderm. The solid, two-lobed anlage of the median thyreoid is connected with the floor of the Trachea constricted off. Undivided bronchial buds. Wolffian duct interrupted cranially, free glomeruli right and left ("pronephric remains"). In the mesonephros anlage of glomeruli, caudally segmental vesicles, partly with rudimentary nephrostomes. Wolffian ducts have reached the cloaca, but do not yet open into it. Very early anlagen of the metanephric buds as enlargements of the Wolffian ducts. Nephrogenic cord. Cloaca with bladder and intestinal bay. Primitive germ cells. Atrial and ventricular septum formed, also the right valvular venous. Primary origin of the aa. umbilicales. The aa. omphalo- mesentericse form a ring around the in- testine. Vv. om- phalo-mesenteri- cae connected by an anastomosis dorsal to the intestine. Upper extremity plate-like, lower one like a swelling. Numerous fresh mitoses.
Remarks - Fixation: (according to Herr, 1893) sublimate- acetic acid ; (according to Jankelowitz, 1895 picric-sublimate-acetic acid. Stain: Borax carmine- aurantia. Sections: 10 μ, trans. The embryo was modelled by Dr. Ingalls, compare Irgalls (1907). Literature: Herr, Beitrag zur Entwicklungageschichte des menschl. Auges. Dissert. Berlin, 1893. Jankelowitz, Zur Entwicklung der Bauch- speicheldruse. Dissert. Berlin, 1895. Also, Ein junger menschlichen Embryo, etc. Arch, f mikr. Anat., Vol. 46, 1895.—O.Hertwig, , LehrbuchderEntwicklungsgeschichte. Also, Elemente der Entwick- lungslehre, 3rd ed., 1907. —Ingalls, N. W., Beschreibung eines menschl.

Embryo, etc., Arch. f. mikr. Anat., Vol. 70. 1907. Bursa omentalis, with foramen of Winslow, is formed.

Reference: Keibel F. and Elze C. Normal Plates of the Development of the Human Embryo (Homo sapiens). (1908) Vol. 8 in series by Keibel F. Normal plates of the development of vertebrates (Normentafeln zur Entwicklungsgeschichte der Wirbelthiere) Fisher, Jena., Germany.
Cited in: 1912 Human Embryology and

Ingalls NW. Description of a human embryo of 4.9 mm (Beschreibung eines menschlichen Embryos von 4.9 mm). (1907) Arch. f. mik. Anat., 70: 506-576.

1908 Embryo Tables: Klb (stage 10) | Pfannenstiel III (stage 11) | Meyer 300 (stage 12) | Strahl 4mm (stage 13) | Hertwig G31 (stage 14)

Template:Human embryo Strahl 6.75mm table

Template:Human embryo Hochstetter Chr 1 table

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Desig.


  • 6 Human embryo Pfannenstiel III. Collection of Prof. PfannenstieL GiesX. T. Fig. Vr and Vv. Textfig. 6a to 6w.



  • 7 Human smbrvo N'o. 300, from the collection of Dr. Robert Meyer, Berlin. H.T. Fig. VI 1, VI r ind VI v.




Age

Body form

Primitive streak

Primitive • _ ments

Chorda

Gr. L. about 2.6 mm.



Embryo bent over the ventral surface and slightly bent spirally.



Tail bud, on its ventral side doubtful remains of primitive streak.



Gr. I 2.5 mm.



Remains of primitive streak. Cloacal membrane.



13-14 Chorda empairs of erging from primi- entoderm, t i v e Cranially is s e g - still in enments. toderm. caudally ; : is probably primarily independent of the entoderm and in this region it is no longer included in the entoderm.


23 Chorda pairs of arated from

pnm. segments.



entoderm.



Nervous - -:em

In brain region medullary canal is open to caudal to the region of the optic vesicle, similarly the caudal end. Anlagen of neuromeres already present.



Anterior neuropore closed. but its position still recognizable. Medullary canal stili wide open for a stretch caudally. Roof of 4th vent, beginning to thin out. Xeuromeres. Trigeminus and acustico-facialis ganglia distinct.



Eve

Ear

Z

Hypophysis

Mouth

Primary optic vesicles. They he close to the ectoderm; in their region the medullary canal is wide open.



Optic vesicles.


Mesoderm between ectoderm and optic vesicle.



Anlage of auditory vesicle recognizable as a thickened and at first but little depressed plate of ectoderm

Hypophysis just indicated.



Auditory vesicle almost closed '.open through 4 or 5 sections of op). Ductus endolymphaticus not yet visible.



Pri pharyngeal membrane still closed. Oral sinus.



Anlage doubtful.



Pharyngeal membrane just 'torn. "still abundant remains i of it. "


liver and pancreas

j. tic ] traee_ patic -.rabeculae.



branchial trachea and lungs.




Heart an . vends




pouches derm, the 3rd is I mned.


anlage" is 8th, of primiti duct. Segmental 11:;. and -



Allantoic Extirpation of uterm fixation: Formaiin sin: Paraearmine.


/dons: 10 *. Recent mitoses *. — — Imntii^mHBn.


ventral connection between pericardial --'-- ^r.'.-.^i. .-.



Intestine still communicates widely wil . the -. sack. L: - : a thick-walled sack from which the trabeculse are beginning to bud.



3 anterior .."!:. .i. pouc: .-•ri :.. •.:.- »:*.::e": '.:.- 4:: reoidea mediana formed. Pulmotracheal groove.


indicated.



" pronephric an- j .


vesi rodi

stomes. Mesonez
connected with fian duct begins to acquire a lumen crania]';. ends enclosed in the ectoderm, still some distance

I strongly zd. An arteries distinct


•rmbryo w&« obtained by operation.


Joum. of Anat. and 41,1907. Also Meyer. Eob. VoL 25. 1904.



988 Desig.



w

o

  • 10 lumas mbryo, 4 im.(lFeb. 895). ol lection f Prof. trahl, iessen. N. . Text-fig. a-9s.




B

Body form

Between Figs. 5 and 7 of His' Normentafel. (The embryo of Fig. 6 of His' Normentafel is probably pathological.) Vertex bend complete. Nape bend has begun.



2 3

On



~

Chorda

Chorda separated from the entoderm, but in the cranial part, through 19 sections, it has as yet no mesoderm below it.



Nervous system

Roof of 4th ventricle thinned out. Neuromeres. In cord no dorsal column and no anlagen of the anterior horns. Branchial cleft organs of the facialis and glossopharyngeus recognizable as placodes.



Eye

The distal wall of the optic vesicle is somewhat thickened and is almost in contact with the ectoderm. A wide communication between the optic vesicle and the cavity of the ventricle. Anlage of the lens recognizable as a thickened epithelial plate.



Ear

The right auditory vesicle c ompletely constricted off and showing the first indications of a ductus endolymphaticus. The left vesicle, which has no signs of a ductus endolymphaticus, is connected with the surface ectoderm by an epithelial cord.



Nose

Hypophysis

Convex Early olfactory anlage areas of hypo less physis.


distinct.



Mouth

Oral sinus, pharyngeal membrane vanished. No tuberculum impar as yet.


Branchial Digestive pouches, thy tract, liver reoid, thymus, and pancreas trachea and lungs

Sagittal stomach enlargement. Hepatic trabecule, but remains of the liver sack still visible. Anlage of dorsal pancreas, not yet very distinct, in region of 6th pair of somites. Very short tail gut. Early anlagen of socalled "glands" iu yolk sack.



Urogenital system

4 branchial pouches reach the ectoderm, all closed, ectoderm and entoderm partly fused. Early anlage of median thyreoid. Tracheal groove. Very early anlage of lung.



"Pronephric" rudiments on right side in region of 8th somite (5th cervical), on left in region of 7th (4th cervical). Mesonephros (anlagen of segmental 1 vesicles and also rudimentary nephrostomes) begins on right in region of 10th, on left in region of 11th somite. Wolffian ducts end independently, thickened and with lumen, close to the ventral surface of the cloaca, near the cloacal membrane. Pronounced intestinal and bladder bay.



Heart and vessels

Heart differentiated into ventricular and atrial portions. Anlagen of trabecular in ventricle. Dist i n c t atrial canal. Posterior mesocardium no longer c o m plete. 1st branchial art, beginning to degenerate in its ventral part, 2nd and 3rd well developed, 4th formed (almost completely on right). Primary origin of aa. umbilicales, secondary one forming. Aorta? fused in region of 5th pair of somites (2nd cervical). A. s u b c 1 a v i a formed.



Integument -5

Hirschland (1899) speaks of an early stage of the milk ridge in this embryo; we would hesitate to give the epithelial thickening in question this

Extremities = B <

Upper limbs un segmented swelling s (Hirschland, p. 235); lower limbs not recognizable in sections. (Hirschland speaks of the "anlage of the as yet very small lower extremities").



Remnrk


Embryo obtained by operation and fixed while fresh. Somewhat compacted mitoses. Fixed in the chorionic vesicle with nitric acid. Stain: Borax carmine. Cut into 3 pieces. Literature: Hirschland, I... lieitrage zur ersten Entwicklung der Mammarorgane b. Menschen. Anat. Hefte, Heft 34-35, 1899, also Inaugural Dissert. Giessen, 1898. Jahrmiirker, E., Ueber die Entwicklung des Speiserohrenepithels beim Menschen. Inaug. Dissert. Marburg, 1906. Recessus and mesolaterale present on right, no recess and no mesolaterale on left.



990 Desig.



  • 14 Human embryo G. 31. Collection of the Anat-biol. Institute, Berlin (Prof. O. Hertwig.) N. T. Fig. VIII. Text-fig. 12a-12p.



Size

Gr. L.= napebreech length, 4.9 mm. Vertex-breech length 4.7 mm. Greatest diameter of yolk sack 0.58 mm.



Si <

Body form



S3 —

a a CO

Between Pigs. 6 and 7 of His' Normentafel, nearer Fig. 7.



Primitive streak

Vanished up to the tail bud.



Prim, segments

35 pairs of segments, the most anterior quite rudimentary.



Chorda

The anterior end terminates close to the hypophysis. Very thin chorda sheath.



Nervous system

Infundibulum. Roof of the 4th ventricle thin. 7 distinct neuromeres in 4th ventricle region. No dorsal columns in spinal cord as yet. Neurenteric cord.



Eye

Transition from optic vesicl e to optic cup. Lens represented by a thickened area of ectoderm. Scattered mesenchyme cells between lens and optic vesicle.



Ear

Auditory vesicle just constricted off. The point of constriction still visible at the ectoderm. Ductus endo lymphaticus just formed.



03

Kft

J3 o S o Q.


73 0) W >> ft o a >> -= CS O u .a >, u 0) >

Mouth

No remains of the pharyngeal membrane. „Tuberculum impar.


Digestive tract, liver and pancreas

tomach anlage lready slightly wisted. Tail gut. ibundant traeculse in liver nlage. Gallladder formed. )istinct anlage f dorsal panreas. Early an\ge of ventral ancreas. (Janelowitz [1895] escribes 2 venral pancreas nlagen. It is oubtful if there re really two; it semed to us lat there was aly one.)

Branchial pouches, thyreoid, thymus, trachea and lungs.



4 branchial . pouches reach 1 the ectoderm. The solid, twolobed anlage of the median thyreoid is connected with the floor of the mouth. Trachea constricted off. Undivided bronchial buds.



Urogenital system

Heart and vessels

Wolffian duct interrupted cranially, free glomeruli right and left ("pronephric remains"). In mesonephros cranially anlage of glomeruli, caudally segmental vesicles, partly with rudimentary nephrostomes. Wolffian ducts have reached the cloaca, but. do not yet open into it. Very early anlagen of the metanephric buds as enlargements of the Wolffian ducts. Nephrogenic cord. Cloaca with bladder and intestinal bay. Primitive germ cells.



Atrial and ventricular septum formed, also t Inright valvula venosa. Primary origin of the aa. umbilicales. The aa. omphalomesentericae form a ring around the intestine. Vv. omphalo-mesenteriese connected by an anastomosis dorsal to the intestine.



srs

z

,3 Extremi '


Remarks.



Upper extremity plate-like, lower one like a swelling.



Numerous fresh mitoses. Fixation: 'according to Hrrr, 1893) sublimateacetic acid; (according to Jankelowitz, 189 picric-Mibiimate-acetic acid.


Stain: Borax carmineaurantia.


Sections: 10 it, trans. The embryo waled by Dr. Ingalls, compare Ingalls 1 1907). Literature: Herr, Beitrng zur Entwicklungsgeschichte des menscnl. Auges. Dissert. Berlin, 1803. — Jankelowitz. Zur Ent wick lung der Bauchspeicheldruse. I>issert. Berlin. 1895. Also, Ein junger menschlichen Embryo, etc. Arch, f mikr. Anat., Vol. 46, 1895.— O. Hertwig, Lehrbuch der Entwicklungsgeechichte. Also, Elemente der Entwicklungslehre, 3rd ed., 1907. —Ingalls, N. W., Beschreibung eines menschl.


Embryo, etc.. Arch. f. mikr. Anat., Vol. 70. 1907.


Bursa omentalis, with foramen of Winslow, is formed.



992 Desig.



  • 21 Human embryo Walther. Collection of Prof. Strahl, Giessen. V T. Textfig. 16a-16s

m

E £

O

<

Body form

The embryo is figured by Hirschland (1899, Plate XIX to XX fig. 2). Somewhat more advanced than the embryo of Fig. 8 of His' Normentafel. Distinct nape and dorsal bends. Maxillary process distinct. Sinus cervicalis wide open. Tail to the right. Slight spiral twisting.



> = b9

Primitive

Nervous

segments Jj system 3

Eye

Ear

Nose

Hypophysis

38 primitive segments, the last not delimited (3 cranial and 35 trunk segments).



Neuromeres in region of 4th ventricle not very distinct. Infundibulum. Cerebral hemispheres indicated. In spinal cord anlagen of the anterior horns distinct, those of the posterior columns are just beginning to form.



Optic cup. No retinal pigment as yet. Stalk of optic cup still very wide. Anlage of lens a flat groove, in which are cell proliferations.



Ductus endo lym phaticus still short and wide.



Flat, and with still somewhat flat olfactory areas.



Wide open hypophyseal sack.



Mouth

Tuberculum impar well developed.

Branchial pouches, thyreoid, thymus, trachea and lungs.



Wide open sinus cervicalis. 4 branchial pouches reach the ectoderm, all closed. Rudimentaryoth pouch. Anlageof median thyreoid connected with the epithelium of the mouth cavity by a long siender stalk. Trachea already constricted off from the oesophagus for some distance. Undivided lung vesicles.



Urogenital system

Heart and vessels

3 a; a

Extrem


GO.



a o 'a § <

Allantois

Remarks.



" Pronephric rudiment" only on the right (in 11th segment = 8th trunk segment). Large glomeruli in mesonephros, quite caudally there are still 3 segmental vesicles unconnected with the Wolffian duct. In about the last 6 tubules the anlage of the glomerulus is forming. Mesonephros begins on right in 11th, on left in 12th segment. Wolffian ducts open into cloaca. Metanephric buds. Metanephric mesenchyme in direct contact with mesonephros, that of right and left come together medially. Large cloaca. Intestinal and bladder bays.



Atrial septum not yet complete. Foramen ovale not yet formed. Left valv. venosa still but little developed, and so the ventricular septum. 1st branchial arch artery completely, 2nd partly obliterated, 3rd, 4th and 6th completely. Aa. subclavian arise at the point of union of the aortic roots. A. coeliaca at level of 10th, a. omphalomesenterica (with two roots) at that of the 13th and 15th segmental arteries. Primary origin of the aa. umbilicales obliterated. Left ductus Cuvieri quite small.


Upper and lower extremities unsegmented stumps.



Allantoic duct in umbilical cord enlarged for some distance

Obtained by laparotomy. Mitoses.


Fixation: Formol. Stun : Borax carmine. Sections: lo /i, trans. Literature: Hirschland, L.. Beitrage zur ersten Kntwicklung der Mammaroi Monschen, Anat. Hefte, Heft 34-35 1899, also Inaug. Dissert. Giessen, 1898. — Jahrmarker, E., Ueber die Entwicklung des Speiserohrenepithels, etc. Inaug. Dissert., Marburg, 1906. 1 )or>al and ventral pillars of the diaphragm, but as yet no pleuroperitoneal membrane. Periesophageal space (recessus superior sacci omenti) in" wide communication with saccus omentalis. g No mesolaterale • sinistrum. ripleen anlage.


  • 28 Human embryo " Chr. l.Col- ^ lection of 3 Prof. Hocli- $ stetter, a Innsbruck. J N. T. Fig. . XIII. Textfig. 20.


Chorda homogeneous from the hypophysis to the tip of the tail, finally united with the tail gut.


Nervous system

7 neuromeres in region of tne 4th vent. Cerebral hemispheres formed. Early anlage of epiphysis. In the spinal cord anterior horns, anterior and posterior columns. About 34 spinal ganglia and 27 spinal nerves. Welldeveloped branchial cleft organs on facialis, glossopharyngeus, and vagus.



Eye

Ear

Optic cup. Traces of pigment in retina. Lens vesicle just closed, point of closure still evident, proximal wall thickened. In interior of lens vesicle scattered degenerating cells, on proximal wall a heap of cells.



Auditory vesicle with rather long ductus endolymphaticus Cabout 300 n long).


Rotation of si a around its i 3 axistf* not yet | pleted. Due 5 almost blocki epithelial pr tions. Simple final loop. Ca spindle-shaped largement. P attachment < vitello-intestin to the intesti ognizable as i enlargement ( lumen. Tail g — ognizable as "a cord from the § to tip of tail, e: •° at end and lumen. Gall solid. Ductus dochus with Pancreatic an still far apart.



lial pouches, lid. thymus, a and lungs.



Urogenital system.



hial pouches be ectoderm, ranchial Median i bilobed, : in left lobe, thyreoglospletely ted.


i constricted onchii giving r first

Heart and vessels.


Reproductive gland indifferent. "Pronephric rudiment" on left side (tubule and "free glomerulus"). Mesonephros at the caudal end with segmental vesicles that have already reached the Wolffian duct. Wolffian ducts open into urogenital sinus after giving off ureters. Renal pelvis roundish. Anlage of cortical portion of suprarenal body.



Septum I not yet complete. Vei anlage of the men ovale. Yalv. venosa dextra and sinistra, septum spurium. Septum ventriculorum still but little developed. Beginning division of truncus arteriosus. 1st branchial arch art. completely obliterated, 2nd interrupted, 3rd, 4th and Gth complete, 5th incomplete. Aortic roots unite between Gth and 7th segmental artery (count by Hochstetter). Post-cardinal veins not yet united by anastomosis ventral to aorta. Anlage of V. cava inferior.


Remarks.


Extirpation of uterus on account of carcinoma. Fresh miti Fixation: Sublimate.


Stain: Alum cochineal.


Sections: 10 n, trans.


Literature: Hochstetter, Ueber die Bildung der primitiven Choanen beim Menschen. Verb. Anat. Ges., 1892; Entwicklungsgeschichte i-nsystems der Amnioten. III. Sauger. Morph. Jahrb., Vol. 1893; Die Entwicklung d. Blutgefasssystems in O. Hertwig's Handb., 1901 and 1903.— Salzer, Entwicklung der Kopfvenen des Meerschweinchens. Morph. Jahrb., Vol. 23, 1895. — Tandler, Ueber die Entwicklung des menschlichen Duodenum in friihen Embrvonalstadien. Morph. Jahrb., Vol. 29, 1900 (1902).— Narath, Der Bronchialbaum der Saugetiere und des Menschen. Bibliotheca med., Part A, Anatomy, Heft 3, 1901.— Keibel, Die Entwicklung der ausseren Korperform, etc., in O. Hertwig's Handb., 1902. — Fuchs, Lehrb. der Augenheilkunde, Leipzig and Vienna, 9th Ed. 1903. — Toldt, Anat. Atlas, 3d Ed., 1903.— Langer, Zur Entwieklungsgescliichte des bulbus cordis bei Vogeln und Saugetieren. Morph. Jahrb., Vol. 22, 1895. — Elze. Beschreibung eines menschlichen Embrvo, etc., Anat. Hefte, Heft 106, 1907. Left mesolaterale in one section. Spleen tubercle.


  • 50 Human embryo No. 250. Collection of Dr. Robert Meyer, Berlin. N. T. Text-fig. 31a-31c.
  • 78 Human embryo Kronig. Keibel's collection. Series No. 1446. N.T. Fig. XXIII v and XXIII i.

Chorda still homogeneous in pelvic region.


Nervous system

Eye

Ear

Nose

Hypophysis

Between Figs. 24 and 25 of His' Normentafel. Locality of the nape bend still indicated. Eyelids beginning to grow over the eyes. Tail knob. Physiological umbilical hernia.


Chorda still homogeneous in region of coccyx.



Stiil indications of neuromeres in region of 4th vent. Epiphysis. Posterior commissure. On the spinal side of post. commiss. still 2 epiphysis-like structures. Medullary canal still extends to the caudal knob.



Optic stalk still open. Abundant retinal pigment.


Lens vesicle % filled, not yet forced away from ectoderm. Early but distinct anlage of ductus nasolacrimalis.



Semicircular canals present as pouches.



Epiphysis with buds. Chiasma. The medullary canal extends to the tail knob into which it is continued as a solid cord.



No lachrymal glands yet. Nasolachrynial ducts and lachrymal canals do not yet reach the epithelium of the nasal cavity or conjunctiva.



Cochlea with | coil. Cartilaginous auditory ossicles. Cartilage in external ear and in auditory meatus.



Primitive choanae closed by the membranffi buccopharyngeal. Primary palate formed. Jacobson's organ.



Infundibu- Prim

Mot

lum and post, lobe of hypophysis. Anterior lobe not yet budded out, connected with the pharynx by a rather narrow duct.



palat

External nares in epithelial anlage. , Upper, middle and lower concha?.



Hypophysis richly budded. Remains of the hypophyseal duct persist.



Pala proc< besid tong Epit papil tong Intri mus< ture tong diffei tiatei Earl; an lag teetr maxi glanc budd out, paro not j sub lingu


estive t, liver ancreas.



i and orrn proScanty is of the it. Anof epibuds in ntestine. ;atic anilmost in inal posi>ut still ^lishable one an


Branchial pouches, thyreoid, thymus, trachea and lungs.


Remains of the sinus cervicalis unconnected with the surface epithelium. Median thyreoid has not yet reached the lateral thymus and lateral thyreoid still connected with pharynx by epithelial cords. Bronchi divided twice.



udinal cular is in agus. lature in ;h, duoand recAnlagen lus in stomeginning ion of mm. lial }f small tie in culum Anus

No cartilage in epiglottis yet. Larynx cartilaginous. Tracheal rings formed of young cartilage. Cartilages of bronchi in preechondral stage. Bronchi divided up to eight times.

Urogenital i em

Integument

Reproductive gland indifferent. Miillerian ductstill short. "Pronephric rudiment" on the left side. Mesonephros with large glomeruli. Renal pelvis budded out. Renal mesenchyme beginning to differentiate. Ureters open into the Wolffian ducts. Cloaca not yet completely divided up (cloacal duct). Suprarenal bodies.



Reproductive gland distinctly an ovary. Lumina of Miillerian ducts not yet connected and ending some distance from the sinus urogenitalis in the genital cord. Well-developed glomeruli in the kidney. Urogenital sinus open.



Septum I complete.


Foramen ovale.


Ostium atrioven triculare commune divided.


Septum ventricu lorum not yet complete.



Anlage of mammary gland clubshaped.



Ventricular septum complete.



On each side a principal anlage of the in a mm a ry gland in the club-shaped stage, in addition hyperthelial structures. No hair anlage yet.



Skeleton

Base of skull and vertebrae pracartilaginous, also ribs and scapula. Humerus, radius, and ulna eartilaginous. Femur pra;cartilaginous.



Terminal phlanges of great toes cartilaginous; in those of the other toes cartilage is not yet distinct. Bone in humerus, femur and tibia. Mandible, maxilla, proemaxilla and palatine ossifying, clavicle osseous and cartilaginous.


Remarks.



Abortion, Mil'.


Stain: Borax carmine.


10 n trans. Pericardial cavity :ir:ite! from pleural cav ities, on the- left ductus pleuro-pericardiacus is losed. Communication between pleural and peritoneal cavities is still wide. Caudal limiting fold (Hochstetter) formed on both sides. Spleen.



Gift from Professor Kronig. Artificial abortion. Mitoses.


Fixation: Zenker's fluid. Stain: Hamatoxylinorange, some sections water-blue-orceinsafranin after Schridde. Sections: 15 tu Perioesophageal space.



998 Desig.



r *S4 Human embr\ 321. Collection of Dr. Robert Meyer, Berlin.

Body form


P4 H

The eyelids have grown over the eyeball for a considerable distance. Very small tail-knob.



Chorda

Chorda is still homogeneous at end of coccyx, shows lateral buds in that region .



Nervous system

Olfactory lobe with evagination of ventricle. Epiphysis with buds. Chorioid plexuses in the lateral and fourth ventricles enormously developed. Medullary canal extends to the coccygeal tubercle, its lumen enlarged towards the end .



Eye

Ear Nose

Hypophysis

Mout

Lachrymal gland formed. Naso-lachrymal ducts do not yet reach the epithelium of the nasal cavity, nor the lachrymal ducts that of the conjunctiva. Beginning differentiation of the retina. Prox. part of the vascular capsule of the lens formed. Endoepithelium on the proximal surface of the cornea distinctly differentiated. Iris, anterior and posterior chambers of the eye.


External nares completely plugged with epithelial proliferation, epithelial knobs projecting from it. Jacobson's organ in connection with the epithelium of the nasal septum by a thin solid cord.



Anterior part of hypophyseal anlage richly budded out. Hypophyseal duct vanished except for doubtful remains.



Palatal ridges b the toi Dental ridges w toothgei Parotid gland b ning to sprout c Submas lary branche Sublingi beginnii sprout Papilla valis, su lingua, ] fimbriat


estive t, liver ancreas

n of ike _ ires in of stomCircular lature hout intes

\illi in lum and : partjof ntestine. lial ir diverin small ae. Anus ised.



Branchial pouches, thyreoid, thymus, trachea and lungs No cartilage as yet in epiglottis. Opening of larynx partly fused. Cartilage rings in trachea and main bronchi. Bronchi divided up to 8 times. Lungs at level of 2nd -9th thoracic vertebrae.



Urogenital system

Reproductive gland a testis. The Miillerian ducts extend to the immediate neighborhood of the urogenital sinus, they are fused to form the genital cord, but their lumina are separate throughout. Doubtful "pronephric rudiment." iMesonephros greatly degenerated. Glomeruli and_ tubuli contorti distinct in metanephros. Smooth musculature of bladder formed. Urogenital sinus open. Sympathetic tissue in centre of suprarenal body. Suprarenals he in region of the 10th thoracic-lst lumbar vertebra, the kidneys in that of the 12th thoracic -3rd lumbar. The mesonephros extends from 1stend of 3rd lumbar, the reproductive gland from lst-middle of 3rd lumbar.



Heart and vessels

Integument

Ventricular septum complete. All the valves formed.



In addition to the principal mammary gland a number of hyperthelial structures on either side, some of which have distinctly the appearance of early stages of mammary gland anlagen. Early hair anlagen in region of eyebrows.



Skeleton

34 vertebrae. Cartilaginous skeleton complete (even in the terminal phalanges of the toes). Mandible, maxilla, praem axilla, palatine, frontal, zygomatic together with squama temporalis osseous. Bone and cartilage in clavicle. Osseous anlagen in humerus, radius, ulna, femur- tibia and fibula.



Remarks.



Mitoses.


in: borax carmine. .Sections: 15 it. Peri oesophageal space not found. Peculiar epithelial grow! ha in the median line of the ventral body wall.



These tables will suffice to give a general idea of the time relations of the development of the various organs. The practical value of the tables is also plainly evident. The investigator who wishes to study some particular organ may quickly determine from the Normentafel what stages he requires for his investigation. And I would place especial importance on the fact that the Normentafel make it possible to estimate the proper value of isolated observations and to assign them readily to their proper jolace.


Furthermore, as may be readily seen when one examines the entire series of Normentafel, in which numerous closely succeeding forms are shown, the tables furnish a measure for the determination of individual variations in the embryonic development of man. Such variations undoubtedly occur, but, as in other amniotes that have been studied, they are not very important. However, the tables also furnish information on more general questions. Even in the preparation of the first Normentafel, that of the pig (published 1897), Keibel (1895) was able to demonstrate that the modification of the time relations, indeed, one may say that overlapping in the development of the various organs is so extensive, that a satisfactory division of the entire development into stages corresponding to a praepiscme form, a fish, a terrestrial animal and an amniote, such as Oppel (1891), for example, has assumed and which must be assumed if the biogenetic law is strictly applicable, such a division is impossible. This was then found to be true for other amniotes that were studied in this way, and especially for man. We see a regular succession of the individual ontogenetic stages only when the preceding stage is the necessary condition for the succeeding one. " The unicellular organism," says 0. Hertwig (1906 2 ), " from its nature, can be transformed into a multicellular one only by cell-division. Consequently in all animals the ontogenesis must begin with a division of the ovum. An organism with definitely arranged celllayers and cell-groups can only be formed from a mass of cells when the cells, during their division, begin to arrange themselves into firm unions. ' : In this sense one may speak, with Oppel (1891), of indispensable stages of development. Otherwise, however, we find in the time succession of the organs no indication whatever of the succession in which they were acquired phylogenetically. It is sufficient to point out that the embryonic organs, the amnion, chorion, and allantoic, appear before other organ anlagen are recognizable. Keibel (1895) has shown that this precocious appearance of various organ anlagen is probably associated with the necessity for their earlier or later activity. That definite traces of the path taken by phylogeny are retained by heredity is, nevertheless, not to be denied, but for the time sucession heredity lias proved to be a force of little moment. That an actual recapitulation of the phylogeny in the ontogeny, and, therefore, the validity of the so-called biogenetic law, is impossible for purely logical reasons Keibel (1893) has already pointed out, when he states that "already in the first member of a developmental series the last one " is determined, and that, consequently, the first member of a series must appear modified, when compared with the first member of another series " which may have had the same phylogenetic beginning, but was completed at a lower stage of development." 3 0. Hertwig (1906?) has termed " this relative dependence between the ovum condition on the one hand and the course and final result of the ontogenesis on the other hand, the ontogenetic law of causation and the parallelism of anlage and anlage product. ' : It follows from this law that all intermediate members will show modifications. These questions, however, need not be further discussed in this place, but I would refer the reader to Keibel (1903) and O. Hertwig (1906 x 2 ). I would call the attention of those who may be interested in comparing the interdependence of the different developmental processes of the human embryo with those of ape embryos to the 9th part of Emil Selenka's Menschenaffen, in which F. Keibel (1906) discusses the external form and degree of development of the organs in ape embryos and has given tables showing the development of the apes in the same way that Keibel and Elze (1908) have shown that of man in the Normentafel zur Entwicklungsgeschichte des Menschen.



Literature

Berry. R. J. A. and Lack, L. A. H.: The Vermiform Appendix of Man and the Structural Changes thei*ein coincident with Age. Journ. of Anat. and Phys., vol. 40. p. 247-256, with 11 figs.. 1906. Borx. G. : Leber Verwachsungsversuche mit Amphibienlarven. Arch, fur Entw. Mech., vol. 4, 1897. (Also published in book form.) Fischel. A. : Leber Variability und Wachstum des embryonalen Korpers.


Morph. Jahrb., vol. 24, 1896. H-uniAE, J. A. : Der gegenwartige Stand der Morphologie und Physiologie der Thymusdruse. Verhandl. d. 16 ten Internat. Med. Kongr. (Ofen-Pesth), 1st section, p. 4-29, 1909. (In this review references are made to results, as yet unpublished, by Hammar's pupils, Hellmann, Kaellmark and Lindberg. ) Hertwig, O.: Aeltere und neuere Entwicklungstheorien. Address delivered at the anniversary of the foundation of the Militar-arztliehen Bildungsanstalten, Aug. 2. 1S92. Berlin. 1892. Hertwig. O. : Allgemeine Biologie. 2nd edition of the text-book Die Zelle und die Gewebe. Jena, 1906 1 .


Compare also Keibel (1898).


Hertwig, 0.: Ueber die Stellung der vergleichenden Entwicklungslehre zur vergleichenden Anatomie, zur Systematik und Descetidenz-theorie (das biogenetische Grundgesetz, Palingenese und Cenogenese). In 0. Hertwig's Handbuch, Jena, 1906 3 . His, W. : Unsere Kbrperf orm und das pbysiologische Problem ibrer Entstebung.


Leipzig, 1874. His, W. : Die Entwicklung der menscblicben und tieriscben Physiognomien. Areb.


f. Anat. u. Pbys. Anat. Abth., 1392. His, W. : Das Prinzip der organbildenden Keimbezirke und die Verwandtschaften der Gewebe. Ibid., 1901. Jonson, A. : Studien iiber die Tbymusinvolution. Die akzidentelle Involution bei Hunger. Arcb. f. mikr. Anat., vol. 73, p. 390-443, witb 12 plates and 11 text-figs., 1909. Keibel, F. : Studien zur Entwieklungsgeschiehte des Schweines (Sus serofa domes tieus) II. Scbwalbe's Morph. Arb., vol. v, 1895. Keibel, F. : Das biogenetisebe Grundgesetz und die Cenogenese. Merkel and Bonnet's Ergbn. der Anat. und Entwicklungsgesch., vol. 7, 1898. Keibel, F. : Ueber den Entwieklungsgrad der Organe in den verscbiedenen Stadien der embryonalen Entwicklung der Wirbeltiere. In Hertwig's Hand bucb, 1906 (appeared in 1903). Keibel, F. : Die aussere Korperf orm und der Entwieklungsgrad der Organe bei Affenembryonen. In Emil Selenka's Menschenaffen, continued by Hu brecbt, Strabl and Keibel. Wiesbaden, 1906. Keibel, F. and Elze, C. : Normentafel zur Entwicklungsgesebicbte des Menschen.


Nornientafeln zur Entwicklungsgesebicbte der Wirbeltiere. Part 8, witb 6 plates and 44 figs, in text, Jena, 190S. Lewis, W. H. : Experimental Studies on tbe Development of tbe Eye in Ampbibia.


1. On tbe Origin of tbe Lens. Aruer. Joum. of Anat., vol. 3, p. 505-536, 1904. Lewis, W. H. : Transplantation of tbe Lips of the Blastopore in Rana palustris.


Amer. Joum. of Anat., vol. 7, 1907. Mehnert, E. : Die individuelle Variation des Wirbeltierembryo. Scbwalbe's Morpb. Arb., vol. 5, 1895. Oppel, A. : Vergleiebung des Entwicklungsgrades der Organe, Jena, 1891. Paton, N. D. : Tbe Relationship of the Thymus to the Sexual Organ. II. The Influence of the Removal of the Thymus on the Growth of the Sexual Organs.


Journ. of Pbys., Cambridge, vol. 32, 1904. Paton, N. D., and Goodall, A.: Contribution to tbe Physiology of the Thymus.


Journ. of Phys., Cambridge, vol. 31, 1904. Rous, W. : Beitrage zur Entwicklungsmechanik des Embryo. VII. Ueber Mosaik arbeit und . neuere Entwicklungshypothesen. Anat. Hefte, vol. 2, Parts 6-7, p. 279-330, 1893. (Alsp Gesammelte Abhandlungen iiber Entwick lungsmech., vol. 2, p. 818, Leipzig, 1895.) Sellheim, H. : Kastration und Knochenwacbstum, Hegar's Beitrage zur Geburtsh.


u. Gynakol, vol. 2, 1899. Soederlund, G., and Backhan, A. : Studien iiber die Tbymusinvolution. Die Altersveranderungen der Thymusdriisen beim Kaninchen. Arch. f. mikr.


Anat., vol. 73, p. 699-725, with 1 plate and 6 text-figs., 1909. Spehann, H. : Ueber Korrelationen in der Entwicklung des Auges. Verhandl.


Anat. Ges. (Bonn), 1901. Suppl. to Anat. Anz.^~ vol. 19, 1901. Spemann, H. : Ueber Linsenbildung bei def ekter Augenblase. Anat. Anz., vol. 23, 1903. Syk, I. : Ueber Altersveranderungen in der Anzahl der Hassal'schen Korper nebst einem Beitrag zurn Studium der Mengenverhaltnisse der Mitosen in der Kaninchentbymus. Anat. Anz., vol. 34, p. 560-567, 1909.


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