780 J. F. GUDERNATSCH 



PSEUDOPLEURONECTES AMERICANUS WALBAUM 



Length of specimen 1^.5 cm. The position of the thyreoid gland 

 in the flounder varies (pi. Ill, figs. 30, 31). In one case it formed 

 a rather compact nodule between the first and second branchial 

 arteries, while in another the main mass was found in the aortic 

 bifurcation between and surrounding the first branchial branches 

 (fig. 20, A). Behind the aortic bifurcation there were only smaller 

 follicles dorsal and lateral to the aorta. The broad base of the 

 deep reaching copula permits only a lateral extension ; thus the 

 thyreoid presents itself as a transverse streak. Small detached 

 follicles lie close to the base of the gills. 



The size of the follicles varies from 15 to 1000/^ in diameter, 

 those of about 200^ being in the majority. There are also a few 

 'giant' follicles. The epithelial cells of the follicles are closely 

 arranged and rather high. The nuclei are oval. The blood supply 

 is rich and lymphatic vessels are well developed. 



