. Carnegie Institution of Washington publication. 98 CHIM^ROID FISHES AND THEIR Fig. 75.âDetail of extia-embryonic region of embryo of fig. 73. e. Ectoderm; "(, mesoblast: '"â¬â (/, //^e^^ glgandc yoIk-celU ; t', vacuole y*-\ yolk-enloderm. have already seen, to the walls of the gut, since it passes to them 3'olk masses, large and small, and perhaps also dissolved yolk material. In evidence of the nutritive value of this material witness numerous mitoses in the adjacent (inmost) cells of the entodermâone of which appears in the present section. In fig. 75 a detail is gi
. Carnegie Institution of Washington publication. 98 CHIM^ROID FISHES AND THEIR Fig. 75.âDetail of extia-embryonic region of embryo of fig. 73. e. Ectoderm; "(, mesoblast: '"â¬â (/, //^e^^ glgandc yoIk-celU ; t', vacuole y*-\ yolk-enloderm. have already seen, to the walls of the gut, since it passes to them 3'olk masses, large and small, and perhaps also dissolved yolk material. In evidence of the nutritive value of this material witness numerous mitoses in the adjacent (inmost) cells of the entodermâone of which appears in the present section. In fig. 75 a detail is given of the process bj^ which yolk-cells are passed into the tissues of the embryo. In this portion of the extra-embryonic blasto- derm the mesoderm occurs only as detached (mesench^-matous) cells (w); the ectoderm forms a single-celled layer, and the entoderm a closely formed cellular mass (jr). Between the entoderm and the yolk is the usual zone of vacuoles {y). At 77teg a large yolk-hlled cell ((/. pp. 83 d scq.) pro- trudes from the yolk into the entoderm, the cells of the latter affording little bar to its progress upward. In this connection we note that the huge cell {meg) lies now within a vacuole in whose wall yolk-nuclei appear; indeed at one point a yolk- nucleus has actually entered the vacuole. In the same figure at 7iicg' is a large cell (cut not quite through the middle) which has evidently had a similar origin to meg] for from its size it can not be confused with a neighboring cell of any germ layer. It contains coarse yolk, and on account of its irregular outline, judging from earlier instances, it has probably undergone division by amitosis. ADDITIONAL EMBRYOS OF THIS PERIOD. A second embryo of this period, i. e., prior to the breaking through of gills and mouth, is shown on plate vii, figs. 42, 42" and 42'', and on plate viii, fig. 42". The present specimen is badly bent in its trunk region, but in other regards it may be readily compared with th
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