334 



Robert J. Terry. 



^ P A 



Fig. 10. Median section of the pineal region of a Salvelinus embryo of 10 mm. 

 H.E.C., series no. 458, section no. 60. X 84. 



Fig. 11. Median section of the pineal region of an Amia embryo of 10 mm. 

 H.E.C., series no. 12, section no. 91. X 84. 



Fig. 12. Median section of the fore-brain of an Opsanus embryo of 5 mm. 

 H.E.C., series no. 110, section no. 55. X 115. 



physeal stalk, the conditions described for the 11 mm. stage obtain 

 in the specimens under discussion. 



Post-velar Arch. Compared with the 11 mm. embryo, the post- 

 velar arch is relatively larger. The evagination is more pro- 

 nounced and there is presented in consequence a considerable 

 posterior surface over which the superior commissure is spread. 

 This relation is very striking in Amia (fig. 11, S). 



