732 J. F. GUDEKNATSCH 



epithelial cells, and thus the colloid forming zone was well defined. 

 This agrees with Htirthle's account, which states that the colloid 

 cells always appear at the same time in a large portion of the wall 

 of a follicle or in several neighboring follicles. The size of the 

 follicles has nothing to do with their appearance. In one case, 

 Siphostoma, the epithehum of all foUicles consisted of cuboidal 

 swollen cells, the nuclei of which were near the cell center or 

 towards the lumen and the cytoplasm was highly acidophile, 

 (pi. IV, fig. 8). 



The normal contents of the follicles is the colloid. It is found 

 in all thyreoids and usually all the follicles contain it; only in a 

 few cases were the majority of them empty. 



In spite of the various ideas expressed in the literature regard- 

 ing the surface irregularities of the colloid there is little doubt 

 that they are caused by shrinkage in fixation. In the majority 

 of follicles the surface of the colloid was perfectly smooth, in 

 some a little retracted from the epithelium, but in others com- 

 pletely filling the lumen. In some foUicles the colloid showed 

 surface indentations. These differences can scarcely be con- 

 nected with the age of the organ, as they were observed in differ- 

 ent stages. In all the young trout, however, the colloid filled 

 the folUcles completely. One possibility is that the content of 

 the follicles does not always possess the same chemical compo- 

 sition, and is influenced bv the same fixation fluid in different 

 ways. 



The view has been held that the true secretion of the cells is 

 hyaline and that it appears in the form of small droplets which 

 are set free on the surface of the cells. This process is thought 

 by some to be responsible for the irregular surfa(;e of the colloid. 

 Two kinds of surface irregularities must be distinguished, first, 

 the large ones which do not correspond with depressions of tlie 

 epithelial cells. These are without doubt due to the fixation. 

 The connecting threads of colloid between the central portion 

 and the epithelium seem to run between the cells and to take 

 hold there. Tangential sections through the folHcle wall, cutting 

 the epithelium just under the free surface, show that the cells 

 do not always lie closely placed in their upper portions and a 



