The Works of Francis Maitland Balfour, Volume 4 (of 4)

Part 1

THE WORKS

FRANCIS MAITLAND BALFOUR.

VOL. IV.

Memorial Edition.

Cambridge:

PRINTED BY C. J. CLAY, M.A. AND SON, AT THE UNIVERSITY PRESS.

Memorial Edition.

THE WORKS

FRANCIS MAITLAND BALFOUR,

M.A., LL.D., F.R.S.,

FELLOW OF TRINITY COLLEGE, AND PROFESSOR OF ANIMAL MORPHOLOGY IN THE UNIVERSITY OF CAMBRIDGE.

EDITED BY

M. FOSTER, F.R.S., PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF CAMBRIDGE;

AND

ADAM SEDGWICK, M.A., FELLOW AND LECTURER OF TRINITY COLLEGE, CAMBRIDGE.

VOL. IV.

PLATES.

London: MACMILLAN AND CO. 1885

LIST OF PLATES, ILLUSTRATING THE ORIGINAL MEMOIRS IN VOL. I.

PAGE

Plate 1. Development of the layers of the blastoderm 29

" Disappearance of primitive groove 41

" 2. Development of blood-vessels 47

" 3.} Preliminary account of development of Elasmobranch " 4.} Fishes 60

" 5. Comparison of early stages of Vertebrates 112

" 6. Development of Elasmobranch Fishes. ch. II. 222

" 7. " " " " III. 246

" 8.} " 9.} " " " " IV. 286

Part 2

" 10. " " " " V. 298 " 11.} " 12.} " " " " VI. 315

" 13. " " " " VII. 361

" 14. " " " " VIII. 378

" 15.} " 16.} " " " " IX. 397 " 17.}

" 18. " " " " X. 446

" 19. " " " " XI. 460

" 20.} " 21.} " " " " XII. 479

" 22.} " 23.} Development of spinal nerves in Elasmobranchs 168

" 24.} " 25.} Structure and development of Vertebrate ovary 549 " 26.}

" 27.} " 28.} Head-kidney in embryo Chick 618

" 29. Early development of Lacertilia 644

" 30.} " 31.} Development of Araneina 668 " 32.}

" 33. Development of paired fins of Elasmobranchii 714

" 34.} " 35.} " 36.} " 37.} " 38.} Structure and development of Lepidosteus 738 " 39.} " 40.} " 41.} " 42.}

" 43.} " 44.} Germinal layers of the Chick 854 " 45.}

" 46.} " 47.} " 48.} " 49.} Anatomy and development of Peripatus Capensis 871 " 50.} " 51.} " 52.} " 53.}

EXPLANATION OF PLATES.

EXPLANATION OF PLATE 1. Figs. 1-5 and 9-12. (II. p. 29.)

Fig. 1. Section through an unincubated blastoderm, shewing the upper layer, composed of a single row of columnar cells, and the lower layer, composed of several rows of rounded cells in which no nucleus is visible. Some of the "formative cells," at the bottom of the segmentation cavity, are seen at (b).

Fig. 2. Section through the periphery of an eight hours' blastoderm, shewing the epiblast (p), the hypoblast (h), and the mesoblast commencing to be formed (c), partly by lower-layer cells enclosed between the epiblast and hypoblast, and partly by formative cells. Formative cells at the bottom of the segmentation cavity are seen at b. At s is one of the side folds parallel to the primitive groove.

Fig. 3. Portion of the hypoblast of a thirteen hours' blastoderm, treated with silver nitrate, shewing the great variation in the size of the cells at this period. An hour-glass shaped nucleus is seen at a.

Fig. 4. Periphery of a twenty-three hours' blastoderm, shewing cell for cell the junction between the hypoblast (h) and white-yolk spheres (w).

Fig. 5. Junction between the white-yolk spheres and the hypoblast cells at the passage from the area pellucida to the area opaca. The specimen was treated with silver nitrate to bring out the shape of the cells. The line of junction between the opaque and pellucid areas passes diagonally.

Fig. 9. Section through the primitive streak of an eight hours' blastoderm. The specimen shews the mesoblast very much thickened in the immediate neighbourhood of the primitive streak, but hardly formed at all on each side of the streak. It also shews the primitive groove just beginning to be formed (pr), and the fusion between the epiblast and the mesoblast under the primitive groove. The hypoblast is completely formed in the central part of the blastoderm. At f is seen one of the side folds parallel to the primitive groove. Its depth has been increased by the action of the chromic acid.

Fig. 10. Hypoblast cells from the hinder end of a thirty-six hours' embryo, treated with silver nitrate, shewing the regularity and elongated shape of the cells over the embryo and the smaller cells on each side.

Fig. 11. Epiblast cells from an unincubated blastoderm, treated with silver nitrate, shewing the regular hexagonal shape of the cells and the small spherules they contain.

Fig. 12. Portion of the epiblast of a thirty-six hours' embryo, treated with silver nitrate, shewing the small rounded cells frequently found at the meeting-points of several larger cells which are characteristic of the upper layer.

EXPLANATION OF PLATE 1. Figs. 6-8 and 13-19. (III. p. 41.)

Part 3

Figs. 6 and 7 are sections through an embryo rather earlier than the one drawn in fig. 8. Fig. 6 passes through the just commencing medullary groove (md), which appears in fresh specimens, as in fig. 8, merely as an opaque streak coming from the end of the primitive groove. The notochord is hardly differentiated, but the complete separation of mesoblast and hypoblast under the primitive groove is clearly shewn. Fig. 7 passes through the anterior end of the primitive groove (pr), and shews the fusion between the mesoblast and epiblast, which is always to be found under the primitive groove.

Fig. 8 is a view from above of a twenty hours' blastoderm, seen as a transparent object. Primitive groove (pr). Medullary groove (md), which passes off from the anterior end of the primitive groove, and is produced by the thickening of the mesoblast. Head fold (pf).

Figs. 13-17 are sections through the blastoderm, drawn in fig. 18 through the lines 1, 2, 3, 4, 5 respectively.

The first section (fig. 13) passes through the true medullary groove (mc); the two medullary folds (A, A) are seen on each side with the thickened mesoblast, and the mesoblast cells are beginning to form the notochord (nc) under the medullary groove. There is no adherence between the mesoblast cells and the epiblast under the medullary groove.

The second (fig. 14) section passes through the medullary groove where it has become wider. Medullary folds, A, A; notochord, ch.

In the third section (fig. 15) the notochord (ch) is broader, and the epiblast is raised in the centre, while the medullary folds are seen far apart at A.

In section fig. 16 the medullary folds (A) are still to be seen enclosing the anterior end of the primitive groove (pr). Where the primitive groove appears there is a fusion of the epiblast and mesoblast, and no appearance of the notochord.

In the last section, fig. 17, no trace is to be seen of the medullary folds.

Figs. 18 and 19 are magnified views of two hardened blastoderms. Fig. 18 is twenty-three hours old; fig. 19 twenty-five hours. They both shew how the medullary canal arises entirely independently of the primitive groove and in front of it, and also how the primitive groove gets pushed backwards by the growth of the medullary groove. pv, Protovertebræ; other references as above. Fig. 18 is the blastoderm from which sections figs. 13-17 were cut.

EXPLANATION OF PLATE 2. (IV. p. 47.)

Fig. 1 is taken from the anterior part of the pellucid area of a thirty hours' chick, with four protovertebræ. At n is a nucleus with two nucleoli.

Figs. 2 and 3 are taken from the posterior end of the pellucid area of a chick with eight protovertebræ. In fig. 3 the nuclei are seen to have considerably increased in number at the points of starting of the protoplasmic processes. At n is seen a nucleus with two nucleoli.

Fig. 4 is taken from the anterior part of the pellucid area of an embryo of thirty-six hours. It shews the narrow processes characteristic of the anterior part of the pellucid area, and the fewer nuclei. Small spaces, which have the appearance of vacuoles, are shewn at v.

Fig. 5 is taken from the posterior part of the pellucid area of a thirty-six hours' embryo. It shews the nuclei, with somewhat irregular nucleoli, which have begun to acquire the red colour of blood-corpuscles; the protoplasmic processes containing the nuclei; the nuclei in the protoplasm surrounding the corpuscles, as shewn at a, a´.

Fig. 6 shews fully formed blood-vessels, in part filled with blood-corpuscles and in part empty. The walls of the capillaries, formed of cells, spindle-shaped in section, are shewn, and also the secondary investment of Klein at k, and at b is seen a narrow protoplasmic process filled with blood-corpuscles.

Fig. 7 is taken from the anterior part of the pellucid area of a thirty-six hours' embryo. It shews a collection of nuclei which are beginning to become blood-corpuscles.

Figs. 1-5 are drawn with an 1/8 object-glass. Fig. 6 is on a much smaller scale. Fig. 7 is intermediate.

Fig. 8. A transverse section through the dorsal region of a forty-five hours' embryo; ao, aorta with a few blood-corpuscles. v, Blood-vessels, all of them being formed in the splanchnopleure, and all of them provided with the secondary investment of Klein; pe, pellucid area; op, opaque area.

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