298 BULLETIN OF THE 



the ectoderm and entoderm alone are capable of giving rise to epithelial 

 tissues. This view, which was associated with the derivation of the 

 urogenital tract from the ectoderm, was naturally revived by Graf Spee 

 ('84). More recent evidence, however, shows that it is only the Wolffian 

 duct in regard to which the question of an ectodermal origin remains 

 open ; the Wolffian tubules, on the other hand, as well as the epithelia 

 of the female sexual tract, are distinctly mesodermal. The statement 

 that epithelia do not arise from the mesoderm is, in my opinion, either 

 insignificant or untrue. If, avoiding genetic characters, we define epi- 

 thelium so narrowly as to exclude endothelium, we must confess that, 

 except in certain specialized regions, epithelia do not develop from the 

 mesoderm ; but the conclusion is obviously of little morphological impor- 

 tance. On the other hand, if we employ broad morphological characters 

 in our definition, such a conclusion is manifestly inaccurate. 



The ectodermal origin of the Wolffian duct has been supposed to 

 account for certain pathological new formations which frequently have 

 their seat in the urogenital organs. Tims His ('G5 b ) saw in the mode of 

 development which he described for the Wolffian and Mullerian ducts an 

 explanation for the occurrence of dermoid cysts in the ovary. It must 

 be confessed that the structure of many of these cysts suggests that they 

 have an ectodermal origin ; but their occurrence in very diverse parts of 

 the body shows that they do not require a normal ingrowth of ectodermal 

 cells into the region in which they arise. Thus in the dermoid cysts 

 which are occasionally found back of the optic bulb, the translocation 

 must be regarded as purely adventitious. 1 



The suggestion has recently been made by Sutton ('8G, p. 344), that 

 testicular and ovarian carcinomata are to be explained by the occurrence 

 of degenerating ducts in the neighborhood of the genital ridge, and he is 

 inclined to regard the Wolffian duct as the means of transporting ecto- 

 dermal cells to this region. The weight of evidence seems to favor the 

 view that carcinomata cannot develop without an epithelial basis (Klebs, 

 '89, p. 771) ; but. this fact does not compel us to seek an ectodermal 

 source for these growths. In the case of adenomata, which also require 

 an epithelial basis, one can see more readily the source of the prolifera- 

 tion ; and these abound in the ovary. The germinal epithelium, in 

 consequence of its retention of embryonic characters, seems to be well 

 adapted to the formation of carcinomata, and, according to Birch-Hirsch- 

 feld's ('89, p. 202) enumeration, they are somewhat more frequent in the 



1 Many dermoids may be explained as eases of foetus in fcetu, and those in the 

 ovary may often be due to extra-uterine gestation. 



