344 



ZnOLOGV 



or in masses, according to the species. The eggs contain 

 much yolk ; consequently the cleavage is partial, and the em- 

 bryo seems to develop on a small part only of the yolk, and for 



Fig. 



Fig. ■ 



Fig. 6. 



Fig. 8. 



Fig. 4. 



Fig. 



Fig. ] 



Fig. 



Fig. 



©Ts 



Fig. 323. — Developmental stages of Sprlrrprs hinnrafus. Figs. l-.>, neural 

 groove beginning to form; Fi(j.\. 0, 7, neural groove closed; Figs. S, 9, 

 head 1:icginiiing to form ; Figs. 10-1 2, tail formed. \'olk a})sorbing ; Fig. 13, 

 embryo eapahle of moving in egg nieinlirane; Fig. 14. embryo just able 

 to swim ; Fig. 1-J. tliree daj's after hatehing. The letters indicate the suc- 

 cessive stages. After H. H. Wilder, fr(jm "The .Vnieriean Naturalist." 



some time after hatching the yolk mass hangs as a lump on the 

 under side of the cmliryo. Very early a deep groove, bounded 

 by a pair of folds, arises on the edge. This groove is large in 



