758 



J. F. GUDERNATSCH 



OSMERUS MORDAX MITCHILL 



A smelt 20 cm. long. This smelt presents the thyreoid condi- 

 tions described below. A few follicles appear far in front of the 

 aortic bifurcation (fig. 8, ^), and further back more are arranged 

 around the copula. At the bifurcation every section shows 

 twelve to fifteen follicles between the stem of the aorta and the 



Fig. 8. Sections through the thyreoid gland of Osmerus. A, anterior to the 

 aortic bifurcation; B, just posterior to it; C, between the first and second; and D, 

 close to the second branchial arteries. 



copula. The follicles vary in size from 40 to 200m. Behind this 

 the main mass of thyreoid tissue lies above the aorta, a few fol- 

 licles lie to either side, and ventral to the aorta they are very 

 scarce. Further back the basibranchiale comes nearer and nearer 

 the aorta, finally reaching it, so that the follicles are forced out 

 laterally (fig. 8, C). In* the region of the hypobranchialia are 



