THE ANATOMY OF THE THYROID GLAND 199 



The colloid cells described by Langendorf ('89) are remarkably 

 distinct in most of the sections of Elasmobranch thyroids and con- 

 stitute one of the most characteristic features of the thyroid gland 

 of these fishes. The colloid cells are distinctly acidophiie and are 

 easily recognized in specimens stained with hematoxylin and 

 eosin if the eosin is used in dilute solution and allowed to act for 

 one-half hour or more. They present a glistening, highly refractive 

 colloid appearance, which is in marked contrast to the granular 

 chief cells. The colloid cells occasionally occur singly, but are more 

 frequently disposed in groups along one side of the follicle. One 

 such group (fig. 14, A), more extensive than the others, was seen 

 to include fulh^ three-fourths of all the epithelium in its follicle. 

 The groups are often in contact with the central colloid mass, and 

 the colloid within the cell may then appear continuous with that 

 within the follicle. Occasionally a group of such epithelium 

 appears to have been completely engulfed by the colloid mass, the 

 epithelial nuclei then appearing well within the colloid. Such 

 appearances might suggest mechanical distortion, but as the sur- 

 rounding follicles show no evidences of injury, and, as already 

 stated, the tissues were very carefully prepared, I am more in- 

 clined to agree with Bozzi ('95) that these appearances are the 

 result of vital phenomena. 



The nuclei of the colloid cells are small and deeply stained, so 

 deeply, in fact, that in the usual preparations they frequently 

 show neither nuclear wall nor karyosomes. Unlike the nuclei 

 of the chief cells thej^ are usually situated near the inner extremity 

 of the cell rather than at its base. The greater the cell is distended 

 with colloid the farther its nucleus is pushed toward the cell's 

 apex; in the most distended cells there was frequently some dis- 

 tortion and even fragmentation of the nucleus. A further continu- 

 ation of this process would account for at least a portion of the 

 extruded and disintegrating nuclei found within the intrafollicular 

 colloid masses (figs. 11 and 18). 



The intrafolhcular colloid closely resembles that of the mamma- 

 lian thyroid gland. It is stronglj^ acidophiie and is usually homo- 

 geneous or very finely granular in appearance. Frequently a 

 minor portion of the mass, e.g., one side, is finely granular while 



