. Journal of morphology . uch as shown in Figs. 2() and III. X 13. Fig. 53. Section through a small portion of the vegetative i)ole of an eggin a slightly earlier stage than that shown in Fig. 51, or about the stageshown in Fig. 25, PI. III. In this stage the surface of the egg seems to indi-cate a total division of all parts into blastomeres, but this section shows thatthe central mass of yolk has not yet become segmented, x 47. Fig. 54. Section of a later stage than Fig. 52, no segmentation cavity, alarge portion of the central yolk cells surrounded by smaller cells, and in oneplace t
. Journal of morphology . uch as shown in Figs. 2() and III. X 13. Fig. 53. Section through a small portion of the vegetative i)ole of an eggin a slightly earlier stage than that shown in Fig. 51, or about the stageshown in Fig. 25, PI. III. In this stage the surface of the egg seems to indi-cate a total division of all parts into blastomeres, but this section shows thatthe central mass of yolk has not yet become segmented, x 47. Fig. 54. Section of a later stage than Fig. 52, no segmentation cavity, alarge portion of the central yolk cells surrounded by smaller cells, and in oneplace there is a considerable down-growth of these smaller cells into thelarger yolk cells. This is a section of the blastopore stage shown in Fig. 28,PI. III. X 13. Fig. 55. Enlarged portion of the invagination shown in Fig. 28, PI. Fig. 50. Bimch of eggs photographed luuler water. Fig. 57. Photograph of later stages of embryos with yolk sac attached. EARLY DEVELOPMENT OF UESMOGNATHUS FUSCA. WILLIAM A. HILTON. PLATE HE Journal of Morphology.—Vol. XX, No. 4. 57 Plate VI. Fig. 58. Section of yolk-plug stage. Dorsal lip above, longitudinal Fig. 59. Late blastopore, early medullary plate stage, longitudinal sectionthrough the blastopore. Shows cavity of the archenteron surrounded by smallcells wath small yolk granules, x ^^^ Fig. 60. Section through the blastopore of stage shown in Fig. 59, showingthe dorsal lip above of two parts, also ventral lip of small cells, x 47. Fig. 61. Section through later medullary plate stage such as shown inFig. 33, PI. III. In this section the beginning central nervous system, thenotochord, mesoderm and small slit of the archenteron may be seen. Nearthe center of the yolk cells is what seems to be a secondary segmentationcavity, x 13. Fig. 62. Dorsal portion of Fig. 61, enlarged. Showing nervous system,notochord, two sheets of mesoderm on each side and cavity of Fig. 63. Caudal end of medullary plate stage showi
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