Bull. U. S. B. F. 1912. 



Plate LIX. 



Fig. 12. — Sa/velinus /ontinalis in sac stage, hatched a few days: showing relation of thjroid follicles to invaeination 

 which becotnes jugular pit. X86. 



'mi' 



lu,. l.s. — i;ruuk truiit lr\ sIiowiiiK early thyroid follicles cuntaininv; cuHoid ni:iteri,il, X^o, 



