Book - The Early Embryology of the Chick 5

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Patten BM. The Early Embryology of the Chick. (1920) Philadelphia: P. Blakiston's Son and Co.

Online Editor 
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This historic 1920 paper by Bradley Patten described the understanding of chicken development. If like me you are interested in development, then these historic embryology textbooks are fascinating in the detail and interpretation of embryology at that given point in time. As with all historic texts, terminology and developmental descriptions may differ from our current understanding. There may also be errors in transcription or interpretation from the original text. Currently only the text has been made available online, figures will be added at a later date. My thanks to the Internet Archive for making the original scanned book available.

By the same author: Patten BM. Developmental defects at the foramen ovale. (1938) Am J Pathol. 14(2):135-162. PMID 19970381

Those interested in historic chicken development should also see the earlier text The Elements of Embryology (1883).

Foster M. Balfour FM. Sedgwick A. and Heape W. The Elements of Embryology (1883) Vol. 1. (2nd ed.). London: Macmillan and Co.



Modern Notes

Chicken Links: Introduction | Chicken stages | Hamburger Hamilton Stages | Witschi Stages | Placodes | Category:Chicken
Historic Chicken Embryology  
1883 History of the Chick | 1900 Chicken Embryo Development Plates | 1904 X-Ray Effects | 1910 Somites | 1920 Chick Early Embryology | 1933 Neural | 1948 Limb | Movie 1961 | Historic Papers

The Early Embryology of the Chick: Introduction | Gametes and Fertilization | Segmentation | Entoderm | Primitive Streak and Mesoderm | Primitive Streak to Somites | 24 Hours | 24 to 33 Hours | 33 to 39 Hours | 40 to 50 Hours | Extra-embryonic Membranes | 50 to 55 Hours | Day 3 to 4 | References | Figures

Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

The Formation of the Primitive Streak and the Establishment of the Mesoderm

The Location and Appearance of the Primitive Streak

The stages of development described in the preceding chapters take place before the egg is laid. The first conspicuous structural feature to make its appearance in the embryo after the laying of the egg is the primitive streak. In eggs that have been incubated about i6 hours the primitive streak is well developed as a linear groove flanked on either side by ridge-like thickenings, extending from the inner margin of the area opaca to approximately the center of the blastoderm (Fig^ 8). The primitive streak lies in the longitudinal axis of the future embryo. The end adjacent to the area opaca is its posterior (caudal) end, the opposite extremity is its anterior (cephalic) end. The cephalic end of the primitive groove is deepened and often somewhat expanded to form a depression known as the primitive pit. Directly anterior to the primitive pit the right and left primitive folds merge with each other in the mid-line to form a small rounded elevation called Hensen's node. Hensen's node is of importance as a landmark rather than because it gives rise to any particular structure.

Patten008.jpg

Fig. 8. Dorsal view ( X 14) of entire chick embryo in the primitive streak stage (about 16 hours of incubation).


As early as the beginning of gastfulation the shape of the blastoderm responds to local inequality in the rate of growth. One of the early manifestations of differential growth is the more rapid extension of the embryo cephalad than either laterad or caudad. This results in a definite elongation in the antero-posterior axis by the time the primitive streak is established (Fig. 8).

The Origin of the Primitive Streak by Concrescence of the Blastopore

The significance of the primitive streak has been the subject of much controversy. The divergences of opinion have been due chiefly to incomplete knowledge of the stages of development passed through prior to the laying of the egg. Our present knowledge of these early stages is, however, sufficient to furnish the basis of an interpretation of the primitive streak which is now widely accepted. This interpretation is outlined below without reference to other, opposed views.

The primitive streak is to be regarded as a scar-like thickening arising from the fusion of the edges^of j the a nterior lip of the blastop^ore. To understand the origin of the longitudinally placed primitive streak from the marginally located, crescentic blastopore it is necessary to follow carefully the growth processes taking place during the closure of the blastopore.

We have already seen how the ingrowth of entoderm from the anterior lip of the blastopore, caused the blastopore to lag behind the other parts of the margin of the blastoderm in the process of radial extension over the yolk surface. During this process the blastopore is compressed from either side toward the mid-line by the rapidly extending margins of the blastoderm adjacent to it and is eventually encompassed by them (see Chap. IV and Fig. 7). Because of the insweeping, converging tendency of the growth which first causes the blastopore to bo laterally compressed and finally causes its margins to grow together the process has been termed concrescence.

A schematic interpretation of four steps in the concrescence of the margins of the blastopore is given in the diagrams of Figure 9. The blastoderm shown in surface- view plan in Figure 9, ^ , is approximately at the same stage of gastrulation as that indicated in Figure 7, J5. To avoid complicating the diagram, the entoderm has not been shown in Figure 9. Numbers have been placed along the lip of the blastopore to facilitate following the changes in position undergone by the points to which they are af&xed. As the margins of the blastoderm adjacent to the blastopore grow, they tend to converge in the direction indicated by the arrows in Figure g, B. The anterior lip of the blastopore is folded on itself by this converging growth. The middle point of the lip, i , comes to lie within the margin of the blastoderm, and points, 2, 2, which formerly lay laterally are brought into apposition in the mid line. Figures C, and D, show how, by the continuation of the same converging growth, the edges of the blastopore are iolded together into a line of fusion at right angles to the original marginal position of the blastopore. At the completion of concrescence, the germ wall of the blastoderm has coalesced posterior to the blastopore leaving the hne along which the blastopore lips have fused within the area pellucida. The non-committal term primitive streak was given to this structure before its origin by fusion of the lips of the blastopore was suspected.


Patten009.jpg

Fig. 9. Schematic diagrams to illustrate the concrescence theory of the origin of the primitive streak. (After Liliie.) For explanation see text.

The Formation of the Mesoderm

In its early condition the primitive streak is a scarcely recognizable thickening of the blastoderm marking the line of fusion of the Ups of the blastopore. The well defined groove with thickened ridges on either side, seen in chicks of 15 to 1 6 hours incubation, is a later development. A new process, the formation of the mesoderm, is taking place at this region and the change in the configuration of the primitive streak is its outward manifestation. It will be recalled that the Up of the blastopore is in all forms a region of rapid cell proliferation. It is a region from which we can trace the addition of cells to the differentiated germ layers, but it is itself indifferent. Ectoderm and entoderm both merge into this indifferent area at the lip of the blastopore. It is impossible 'to fix, except arbitrarily, where ectoderm begins and entoderm ends. Later when the mesoderm appears, we can trace the origin of its cells directly or indirectly to the same area of indifferent, rapidly proliferating cells. It is therefore wholly in line with the embryology of other forms to find the mesoderm of the chick arising at the fused lips of the blastopore.

The manner in which the mesoderm arises can be understood only by the study of sections or diagrams of sections. Figure 10, A, represents schematically the conditions which would be seen in a section cut in the line b-b across the marginal notch of an embryo of the stage depicted in Figure 9, B. The margins of the blastopore at the point where this section is located have been folded so they lie in close proximity to each other. A little later they would be fused as shown m Figure 10, B. At the region of fusion, that is to say at the primitive streak, the entoderm and ectoderm merge in. a mass of rapidly dividing cells (Fig. 13, Z>). A section across the primitive streak at a somewhat later stage (Fig. 10, C) shows cells extending to either side of the undifferentiated cell mass, between the ectoderm and the entoderm. These cells are the primordium of the third of the germ layers, the mesoderm. The outgrowth of the mesoderm and the median depression in the primitive streak appear synchronously. This mediae depression in the primitive streak is the primitive groove. It is not unlikely that the formation of the primitive groove is due to cell rearrangement in this region entailed b/ the rapid outgrowth of the cells constituting the mesoderm. (See arrows in Figure10, C.)

Patten010.jpg

Fig. 10. Diagram showing schematically the relations of the germ layers during the formation of the primitive streak by concrescence of the margins of the blastopore.

A. Hypothetical section of blastoderm at the stage represented in Fig. 9, B. Tilp plane of the section is indicated by the line b-h Fig. 9, B. B, hypothetical section of blastoderm at the stage represented in Pig. 9, D. The plane of the section is indicated by the line d-d. Fig. 9, D. C, schematic transverse section through the primitive streak at the stage represented in Fig. 8.

With the formation of the mesoderm the chick has established the three germ layers characteristic of all vertebrate embryos. The importance of these layers lies in the uniformity of their origin and histdlity. From them the development of all the organ systems may be traced. The ectoderm gives rise to the outer epithelial covering of the body and its derivatives (feathers, claws, skin glands, etc.) , the nervous system, and the sense organs. The entoderm gives rise to the epithehal Uning of the digestive tube and of the respiratory organs and the epithelium of their associated glands. The mesoderm becomes differentiated to form the fibrous and rigid connective tissues (except neuroglia) the muscle, the epithelial Uning of the body cavities, the organs of the circulatory system, the blood, the lymphatic organs and the major part of the urino-genital system of the adult.


Next: Primitive Streak to Somites



The Early Embryology of the Chick: Introduction | Gametes and Fertilization | Segmentation | Entoderm | Primitive Streak and Mesoderm | Primitive Streak to Somites | 24 Hours | 24 to 33 Hours | 33 to 39 Hours | 40 to 50 Hours | Extra-embryonic Membranes | 50 to 55 Hours | Day 3 to 4 | References | Figures | Site links: Embryology History | Chicken Development


Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

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Cite this page: Hill, M.A. 2017 Embryology Book - The Early Embryology of the Chick 5. Retrieved December 18, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_The_Early_Embryology_of_the_Chick_5

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G