GD 
FIG. 216 
SINAN AG A 
whe 
aut 
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OR ddrdtatee 
ake 
my 
9D). 
a Ni veer = 
Pere’ 4 
5 ae 
8 es 
YA — 
Figs. 216-230. — Development of shark, Scy//ium (mainly). (All but 216 after BAL- | . 
vouns 216. Egg freed from case showing germ disc GD. 217. Germ discatsecond | 
cleavage. 218. Germ disc at fifth (?) cleavage. 219. Vertical section of similar 
220. Vertical section of slightly older germ disc. 221. Blastula, 222, Early a 
223. Blastoderm showing early growth of embryo. 224-226, Sige later stages 
of embryo. 227. Stage showing early embryo and mode in which the blastoderm sur- | 
rounds yolk. 228. Early embryo viewed as a transparent object. 229, 230. Transverse - 
sections of early embryo. 
A. Anal invagination. AU. Auditory vesicle. BP. Dorsal lip of blastopore. GC. 
Ceelenteron. CF, Tail folds. CH. Notochord. CP. Cephalic plate. ZC. erm. — 
EN. Entoderm. G. Gut. GD. Germ disc. GS. Gill slits. A. Heart. AA. Head — 
eminence. MM, Central nervous system. /’, Yolk nuclei, merocytes. M2#S, Mesoblast. — 
NC. Neurenteric canal. OP. Optic vesicle. PS. Primitive segments, S$. Mouth pit, — 
stomodzeum, SC, Segmentation cavity. 
194 ‘ 
