THYREOID GLAND OF THE TELEOSTS 751 



CRISTIVOMER NAMAYCUSH WALBAUM 



Length of specimen, 12 cm. The outlines of the thyreoid region 

 in the great-lake trout are about the same as in the former spe- 

 cies, but the ventral and posterior extensions are more limited. 

 The anterior end lies in front of the aortic bifurcation, the pos- 

 terior end at the third branchial arteries, (pi. II, fig. 24). The 

 conditions from the aortic bifurcation to the second branches 

 are the same as described in the species above but at the second 

 arteries the accumulation of thyreoid material is rather large. 

 Here also are found the largest follicles. The lateral extension is 

 wider than at the first branches. The aorta is surrounded by 

 follicles (fig. 5, D) but they do not lie very close to its wall. Pos- 

 teriorly the extension decreases, three to four follicles being seen 

 in a section above and below the aorta. The ventral follicles 

 soon disappear and at the third aortic branches the dorsal ones 

 also run out. 



The follicles are a little larger than those of the black trout. 

 Irregular and circular cross sections of the follicles are seen, 

 the latter 20 to 100^ in diameter. The epithelial cells are gen- 

 erally cubical, about 6/1 high. The nuclei are circular, 3ju in 

 diameter, oval or somewhat irregular. The bent nuclei des- 

 cribed in the black trout are present, but not so numerous. Some 

 follicles show only regular nuclei, others only irregular, so that 

 one might imagine these forms associated with different physi- 

 ological stages. Almost all the follicles contain colloid. 



There are many capillaries in the fatty tissue in close contact 

 with the follicles. The follicles are not located on large veins 

 and only a few lie close to the lymph sinuses. 



SALVELINUS FONTINALIS L. 



Length 4 cm., age 1 month. In this young brook trout the thy- 

 reoid gland has not developed very far, certainly not so far as 

 Maurer describes for this stage. The folhcles are scarce, the most 

 anterior lying in the aortic bifurcation. Between the first and 

 second branchial arteries there are a few follicles in each section, 



