404 WALTER E. CAMP 



Acanthias the body may, primarily, arise symmetrically on the 

 two sides but that the right gland rapidly atrophies and dis- 

 appears. Greil ('05) in his work on selachians found the body 

 present only on the left side. From these observations and 

 from the fact that the right gland, when present, appears rela- 

 tively late (33 mm. or later) and is always represented as a single 

 small vesicle, it is very probable that it entirely degenerates in 

 the course of development. 



If the mode of development of the suprapericardial body be 

 carefully analyzed, it will be found that it differs both from 

 the ordinary type of branching gland ( tubulo-alveolar) and the 

 typical closed-follicular ductless gland. The ordinary type of 

 gland in selachians develops- as a direct outpouching of the 

 epithelium. This outgrowth is usually preceded by a thicken- 

 ing of the epithelium to form a gland bud, as has been described 

 in the gastric glands by Peterson ('08), in the pancreas and 

 liver (Scammon '14; '15) and in the digitiform gland (Hoskins 

 '15). The blind extremity of this outpouching gives rise to the 

 tubular or saccular end pieces while its connecting-stalk forms the 

 excretory canal. The end pieces may become secondarily removed 

 from the main excretory duct, but they always remain in com- 

 munication with it (fig. 20, A, 1. 2, 3). The ductless glands, 

 typical examples of which Laguesse ('10) has described as glands 

 with closed follicles, develop as an outpouching of the epithelium 

 which almost immediately becomes solid. This solid anlage be- 

 comes broken up into cell-cords or plates (Norris '16) which ac- 

 quire lumina and develop into follicles or vesicles, the most of 

 which are completely closed (thyreoid, fig. 20, C, 1, 2,3). The 

 connecting-stalk or excretory canal usually entirely disappears 

 in most forms early in the development. Occasionally, however, 

 vestiges of the original duct are found. In the thyreoid of man 

 these vestiges form accessory thyreoid masses or develop into 

 cysts or tumors. Goodey ('10) has described vestiges of the 

 original thyreoid evagination in Chlamydoselachus anguineus, 

 Scyllium catulus and Scyllium canicula, in the form of a small 

 duct or a mass of accessory thyreoid follicles which occupies a 

 foramen in the basibranchial cartilage immediately above the 



