THYREOID GLAND OF THE TELEOSTS 771 



STENOTOMUS CHRYSOPS L. 



Length of s-peciinen 25 cm. The scup presents the thyreoid gland 

 as a rather continuous organ, only one group of follicles lying 

 below the aorta is isolated from the main mass. The largest 

 expansion of the gland is in (fig. 15, A) and immediately behind 

 the aortic bifurcation ; here it measures 3 mm. in width, and dorso- 

 ventrally over 1 mm. This expansion is followed by a restriction, 

 the folhcles always lying above the aorta. At the second branchial 

 arches another increase in the thyreoid tissue occurs, and here 

 a few follicles appear below the aorta (pi. I, fig. 14). 



The size of the generally circular follicles varies from 20 to 

 300/i in diameter, a few reaching 40()/x. 



CYNOSCION REGALIS BLOCK 



Specimens of 60 cm. in average length. Twelve specimens of 

 the squeteague were examined and they serve to show a series 

 of variations in the thyreoid gland within the species. The region 

 of the gland extends from in front of the aortic bifurcation to the 

 third branchial arteries. The majority of follicles always lie 

 either dorsal or lateral to the aortic stem and in only two cases 

 were any follicles found below the aorta. In one case the aortic 

 stem between the first and second branches was surrounded. The 

 region of the second aortic branches is commonly filled by the 

 gland. The tendency to extend from this place anteriorly is 

 more often expressed than in the opposite direction. The lateral 

 extension is greater along the branchial arteries than in inter- 

 mediate regions (pi. Ill, figs. 31-41). 



In some of the specimens there were two (pi. Ill, figs. 33, 36, 

 37, 40) or even three and four (pi. Ill, fig. 34) well developed 

 isolated portions of the gland lying on different branches of the 

 gill vessels. Macroscopically they appear to be separated, but on 

 tracing the entire region in serial sections it is found that follicles 

 spread out and connect the several masses, although the follicles 

 are small and scattered so thinly that they were not seen with the 

 naked eye. 



