728 J. F. GUDERNATSCH 



Branched follicles are particularly abundant in some species. 

 In Muraenoides all follicles seem to branch. Baber states that 

 in young animals the folhcles are much more ramified than in 

 older ones; he, therefore, regards this branching as the method of 

 follicle multiplication. Anderson, on the other hand, holds the 

 'melting' of the epithelium (a process about which I shall speak 

 later) at the point where two follicles meet responsible for the 

 communication between several lumina; this of course is an oppo- 

 site process from that of budding. Anderson, therefore, believes 

 that in old animals there are more irregular follicles than in the 

 young. It seems to me that the ramification of the follicles does 

 not depend so largely upon age, but rather on the species. 



The follicular epithelium varies but little with the species, 

 perhaps the number of cells ma}^ differ in follicles of the same capa- 

 city. The epithelium is of the form usually found in the thyreoid 

 glands of higher vertebrates. All transitions exist from a pave- 

 ment epithelium of very low broad cells, through cuboidal cells 

 as high as broad, to very high and narrow cylindrical cells (pi. 

 V, fig. 10). - 



The form of the epithelium is probably connected with the age 

 of the specimen, as it undoubtedly flattens with increasing age. 

 (In very old human subjects only perfectly flat cells have been 

 found.) Age, however, can scarcely be the only factor, as in some 

 species diiferent forms of epithelium appear at the same time. This 

 may be due to the different ages of the follicles, though it cannot 

 be regarded as an absolute rule that the older follicles have a lower 

 epithelium than the younger. Hiirthle definitely states that 

 these two factors are independent of one another. Langendorff 

 points out that the follicles increase in size, not by a flattening 

 out of the epithelium, but by multiplication of cells. I should 

 say that both processes may be simultaneously involved since we 

 often find large follicles with high epithelium, yet karyokinesis 

 is rarely observed in the epithehal cells. The latter fact led 

 Stockard to suppose that amitotic cell division might occur in the 

 growing thyreoid tissue of Bdellostoma. 



The different types of epithelium might be accounted for in 

 still another way by supposing the follicles to be in different 



