BULL. U. S. B. F. 1912. 



PLATE LIX. 



FIG. 12. Salvelinus fontinalis in sac stage, hatched a few days; showing: relation of thyroid follicles to invagination 

 which becomes jugular pit. X86. 



Fi<;. 13. Brook trout fry showing early thyroid follicles containing colloid material. XS6. 



