EXPLANATION OF PLATE IV 



Plates IV and V, Photographs of the histological features of the thyreoid gland 

 in different species. 



1 Brevoortia. Two follicles with their epithelial cells drawn out into spinous 

 processes. Dia. 1: 165. 



2 Brevoortia. Two follicles, F (the right one containing colloid), and a large 

 lymph vessel, L, between them. The content of the vessel shows similar droplets 

 to those sometimes seen on the surface of colloid, and believed by Anderson to 

 contain the 'chromophobe' secretion. Dia. 1:350. 



3 Brevoortia. An isolated follicle, F, in the most anterior portion of the thy- 

 reoid, with neighboring lymph vessels, L. Dia. 1 : 160. 



4 Brevoortia. General view of the thyreoid in the osseous capsule. Dia. 

 1:60. 



5 Brevoortia. Degenerating epithelial cells and their basal processes. F, 

 Follicular lumen, E, Epithelium. Dia. 1: 700. 



6 Fundulus heteroclitus. Two pictures showing numerous small capillaries, 

 Ca, deeply buried in the epithelium, E, of the follicles, F. In the lower picture the 

 epithelium has retracted slightly from the endothelium. A, ventral aorta. Dia. 

 in a, 1:134; inb, 1:345. 



7 Siphostoma. A general view of the posterior end of the thyreoid gland. 

 Ph, pharynx; A, ventral aorta; F, follicles; Ca, capillaries. Dia. 1: 34. 



8 Siphostoma. Single follicles, F, with their colloid forming epithelial cells, 

 but containing no colloid. Ca, capillaries. Dia. 1: 345. 



9 Oncorhynchus. Irregular nuclei, N, of the epithelial cells. E, epithelium of 

 a follicle viewed from the top. Dia. 1 : 650. 



