742 J. F. GUDERNATSCH 



CLUPEA HARENGUS L. 



In the herring (specimens 30 cm. long) the thyreoid gland is 

 well developed (pi. I, fig. 2). The triangular region formed 

 between the floor of the pharynx, bases of the first gill arches and 

 a ventrally lying cartilage is entirely filled with follicles. The 

 distance between the floor of the pharynx and the ventral mus- 

 culature is considerable, while the cartilages of the basibranchiale 

 are only slightly developed; there is thus sufficient space for a 

 dorso-ventral distribution of the thyreoid follicles (fig. 2, A, B). 

 In certain places the first gill arteries are completely surrounded 

 by follicles ; this is also true of the ventral aorta behind the anter- 

 ior bifurcation (fig. 2, B). Back of the second branchial arteries 

 the extension of the gland diminishes, and only small follicles 

 make a complete ring around the aorta, from which rays of fol- 

 licles go out towards the cartilages and muscles. 



The average size of the follicles is about 200m in diameter; 

 very large ones are not seen. The follicular epithelium is in gen- 

 eral rather high and varies between narrow cylindrical cells to 

 broad cubical ones. The cells are not very densely arranged. 

 In some regions are found a few neighboring follicles with high 

 epithelial cells which almost obliterate the central follicular 

 space (pi. V, fig. 20, Coz). Other follicles have lower cells and 

 all stages exist between these and the normal ones. This suggests 

 a zone of Hiirthle's colloid-forming cefls. The cytoplasm is highly 

 eosinophile and the nuclei are located near the inner surface of 

 the cells. In the intermediate stages, where there is a lumen in 

 the center of the follicle we find in it colloidal material and red 

 blood corpuscles. 



BREVOORTIA TYRANNUS LATROBE 



In this species (length 40 cm.) there are very interesting con- 

 ditions in the extension of the thyreoid gland, due to the enor- 

 mous elongation of the gill region. The distance from the heart 

 to the anterior aortic bifurcation measures about 5 cm. and with 

 this stretching of the ventral aorta the thyreoid becomes extended 

 over a long region. The front end of the gland lies well beyond 



