754 J. F. GUDERNATSCH 



branchial arteries a small accumulation of thjTeoid tissue once 

 more appears. 



A second series shows conditions similar to those above de- 

 scribed. The follicles in the anterior region are less densely 

 arranged. The basibranchiale comes very close to the aorta and 

 separates to some extent two portions of thyreoid tissue along 

 the aortic stem. The follicular mass is little reduced behind the 

 aortic bifurcation but a little in front of the second branchial 

 arteries the typical restriction is found. At this place the first 

 ventral follicles appear. When the second aortic branches are 

 reached the lateral extension of folhcles becomes very wide. 

 The mass of thyreoid tissue is here much increased, and the 

 ventral portion is well developed but not so far as in the trout 

 described above. The thyreoid stops close behind the second 

 branchial arteries. 



In a third series the separation of follicles in the anterior por- 

 tions is still greater than described in either the first or second. 

 The dorsal limit reaches to the upper edge of the basihyale, 

 where there is an accumulation of folUcles on both sides. The 

 first branchial arteries are for a long distance completely sur- 

 rounded by follicles, but the number of follicles decreases visibly 

 towards their union; thus in this case there is an accumulation of 

 follicles in front of the first aortic bifurcation. The ventral fol- 

 licles appear at the first branchial arteries and disappear before 

 reaching the second. It seems that here the entire thyreoid mass 

 is pushed much farther towards the head than in the other trout 

 described. Between the first and second branchial arteries the 

 conditions are similar to those in the other specimens, the distri- 

 bution of the folhcles being restricted. There is no pronounced 

 increase of thyreoid tissue or lateral distribution at the second 

 branchial arteries and the posterior limit of thyreoid follicles is 

 in front of the third branchial arteries. 



High epithelial cells were predominant in the folhcles of all 

 the thyreoids. The cubical cells measure 9 to lO/x broad and 

 12)u high, and the narrow cylindrical cells are 2 to 3)u broad 

 and 20m high. The nuclei are usually large and round, except 

 in the very high cells where they are compressed. In a few places 



