THYREOID GLAND OF THE TELEOSTS 727 



The form of the follicles is also variable, most typical perhaps 

 are the globular or elliptical and tubular types. The smaller 

 follicles are nearly always circular in section (pi. V, figs. 10-12), 

 especially when they are free. The shape of the more closely 

 packed follicles is influenced by pressure, and may be fiat, in- 

 dented, or irregular in outline. When the follicles lie next to the 

 cartilages or muscles they are usually oblong-oval, with the longer 

 side towards the tissue. Single follicles lying in the supporting 

 tissue, if large, are rarely prefectly circular, but have irregular 

 outlines due to pressure from the fibres of the substratum. The 

 shape of these follicles indicates the existence of actual pulling 

 forces in the supporting tissue. 



Not only small irregularities are found in the surface of the 

 foUicles, but also deep invaginations of the epithelium as well 

 as long evaginations. The follicle may consist of a central body 

 with sprouts or branches of cyhndrical and globular shapes (pi. 

 V, figs. 15, 16). How far these irregularities in form are connected 

 with the cutting off of smaller follicles from larger ones could not 

 be determined. Anderson doubts the multiplication of foUicles 

 by such a process. 



It is now generally accepted that no communication from folUcle 

 tofoUicle exists; the foUicles are closed on all sides and perfectly 

 separated from each other. Sometimes, however, as many as five 

 follicles are observed in a section, apparently perfectly separated, 

 but on tracing through the series of sections they all unite into 

 one foUicle (pi. V, fig. 16). This is due to evaginations from 

 the foUicular wall somewhat like the fingers of a glove, which when 

 cut across, give the appearance of several independent foUicles, 

 while in reality there is only one lumen. In Anguilla chrysopa, 

 however, there really seemed to be a communicating duct between 

 two foUicles ; the lumen of the tube was much narrower than that 

 of the follicles and the epithelial cells of it were much higher 

 (pi. V, fig. 15). This closely resembles a ' Schaltstiick' as seen in 

 other glands. This was not due to a waist-like constriction of the 

 epithelium, but to a far reaching evagination from one follicle with 

 a globular swelling on the free end representing a second follicle. 

 There was no colloidal substance in the 'intercalary' duct. 



