Bull. U. S. B. F. 191 2. 



Plate LXIII. 





Fic;. 19. — Domesticated Scotch sea trout tiiigerling; normal thyroid structure. Xs 



Fig. 20. — Domesticated Scotch sea trout fiiiEerlillE: same liatcher.v as above, showing simple hyperplasia, increased 

 number of thyroid follicles; epithelium high cuboidal and low columnar: colloid diminished. X86. 



