DEVELOPMENT OF TELEOST 211 
from their intimate relations with the yolk, are supposed 
to subserve some function in its assimilation. 
Aside from the question of periblast, the growth of 
the blastoderm appears not unlike that of the sturgeon. 
From the blastula stage of Fig. 273 to that of the early 
gastrula (Fig. 275), the changes have been but slight ; the 
blastoderm has greatly flattened out as its margins grow 
downward, leaving the segmentation cavity apparent at 
SC. The rim of the blastoderm has become thickened, 
as the ‘germ ring;’ and immediately in front of ABP, the 
dorsal lip of the blastopore, its thickening, as in Fig. 255, 
marks the appearance of the embryo. In Fig. 276 the 
germ ring, GR, continues to grow downward, and shows 
more prominently the outline of the embryo; this now 
terminates at AHP, the head region; while on either side 
of this point spreads out tail-ward on either side the indefi- 
nite layer of outgrowing mesoderm, JES. In the stage 
of Fig. 277 the closure of the blastopore, BP, is rapidly 
becoming completed; in front of it stretches the widened 
and elongated form of the embryo. A sagittal section 
through a late stage of the blastopore appears in Fig. 278; 
with it may be compared the corresponding region of the 
sturgeon of Fig. 256; the yolk plug, Y/, of the latter is 
now replaced by periblast, P, the dorsal lip at BP, by 
TM, the tail mass, or more accurately the dorsal section 
of- the germ rim; the ccelenteron under the dorsal lip 
has here disappeared, on account of the close approxima- 
tion of the embryo to the periblast; its last remnant, 
the Kupffer’s vesicle, KV, is shortly to disappear. At 
TM, the germ layers become confluent as at BP in Fig. 
256, but, unlike the sturgeon, the flattening of the dorsal 
germ ring, 7, does not permit the formation of a neu- 
renteric canal. 
