496 



BERTRAM G. SMITH 



bip. 



vp- 



MP' 



34 



35 



biD. 



36 



37 



Fig. 134 Diagram of an egg of Cryptobranchus alleghenionsis in the beginning 

 gastrula stage viewed from the lateral aspect, showing average amount of rotation, 

 and the positions of the beginning blastopore and the septal furrow; blp., blasto- 

 pore; m, morphological axis; s.f., septal furrow; v, vertical axis determined by 

 gravity; v. p., vegetal pole. 



Fig. 135 Similar diagram of a gastrula at the time when the blastopore reaches 

 the form of a semicircle. Lettering as before. 



Fig. 136 Similar diagram of a gastrula at the time when the blastopore first 

 becomes a complete circle. Lettering as before. 



Fig. 137 Combination of the preceding diagrams. The egg is shown in the 

 posi*^ion assumed at the close of the period considered. The black band indicates 

 the amount of overgrowth of the dorsal lip of the blastopore (42 degrees); blp., 

 blp'. and hlp^, mark the successive positions of the dorsal lip of the blastopore; 

 s.f. and s./.', successive positions of the septal furrow;/, i)osition of the vanishing 

 fenestra. Other lettering as in the preceding figures. 



