755 



J. F. GUDERNATSCH 



ONCORHYNCHUS KISUTCH WALBAUM 



Specimen 6 months old, 7 cm. long. The thyreoid gland in the 

 silver salmon extends further back than in most of the trouts, 

 reaching beyond the fourth branchial arteries (pi. V, fig. 20). 

 Another feature in the arrangement is that the follicles lie rather 

 close together, surrounding the stem of the ventral aorta through- 



Fig. 7. Sections through the thyreoid gland of Oncorhynchus. A, just posterior 

 to the aortic bifurcation; B, at the second branchial arteries; C, posterior to the 

 third branchial arteries. 



out almost its entire length. The amount of thyreoid tissue is 

 small at the aortic bifurcation and between the first and second 

 branchial branches (fig. 7, A). At the second gill artery the thy- 

 reoid tissue is most abundant. 



