DEVELOPMENT OF TELEOST 207 
chian in character, are appearing. An embryo shortly 
before hatching is next figured (Fig. 264); the head has 
now entirely lost its flattened character; the mouth in- 
vagination occurs at J/; the tail, much elongated, is 
compressed laterally, and already presents the dermal 
embryonic fin; the yolk sac is attached along the an- 
terior body region, in a position more nearly that of the 
shark than of the lung-fish. 
Of the two Ganoids, sturgeon and gar-pike, the latter, 
as the writer has pointed out, * has the more shark-like 
developmental features. Its segmentation is incomplete, 
since the yolk pole of the egg is at no time traversed even 
by superficial furrows. The blastoderm, or cell cap, is 
“early apparent, and is clearly marked off by a furrow from 
the irregular marginal blastomeres (Fig. 265). It resem- 
bles closely the segmented germ disc of an Elasmobranch, 
and the irregular marginal blastomeres may be compared 
to merocytes. The section of a late blastula of Fig. 266 
does not differ widely from that of the shark of Fig. 221; 
a segmentation cavity is present, whose floor is smooth, 
and contains a well-marked zone of merocytes, 7; the 
smaller quantity and firmer consistency, perhaps, of the 
yolk do not, on the other hand, permit the blastula to 
occupy the sunken position of that of the shark. In the 
gastrula of the gar, further, a well-marked notch appears 
at the dorsal lip (as in this stage, Fig. 223, of the shark), 
representing the primitive blastopore. And, finally, the 
form of the embryo rises boldly from the surface, and 
early presents the well-marked head and tail eminences, 
HE and 7, of Fig. 268, comparable with Figs. 225 and 
227. 
* Am. F. Morph., Vol. X1, No. I. 
