E. H. Whitehead 171 



plasm." " In the ovary of the 85 day rabbit they are very common, 

 their origin from the theca interna of atretic follicles being clearly 

 shown. This, taken in connection with the additional fact that they 

 make their appearance in the 3.5 cm. pig embryo coincident with the 

 fatty degeneration of the germinative cells of the seminiferous tubules 

 and their ovarian homologues, together with that of many cells of the 

 germinal epithelium, would lead us to conclude that cell-degeneration 

 offers the stimulus or condition that brings about the formation of the 

 interstitial cells." 



The observations about to be described were made upon pig embryos. 

 The material was fixed principally with Zenker's fluid, and stained with 

 haematoxylin and Congo-red, iron-hgematoxylin and Congo-red, and by 

 Mallory's method for connective tissue. A series was fixed in Flem- 

 ming's fluid, and studied either stained with iron-hsematoxylin or un- 

 stained. Another series was used for frozen sections and staining with 

 Sudan III. Also a few other methods were employed for special pur- 

 poses. 



It should be remarked at the outset that the theory that Leydig's cells 

 are derived from the epithelium of the Wolffian body cannot obtain in 

 the pig; for in this animal Leydig's cells appear before connection has 

 been made between the epithelial constituents of the testis and Wolffian 

 body. Furthermore, in the case of the pig, at least, the tubules of the 

 rete testis grow into the Wolffian body and establish connection with 

 the Bowman's capsules of the glomeruli, and not vice versa. In this 

 connection see also J. B. MacCallum : Notes on the Wolffian Body of 

 Higher Mammals; Amer. Jour. Anat., Bait., Vol. I, No. 3, p. 245; and 

 the article of Allen previously referred to. 



As I find myself in accord with the conclusion of Allen, that the inter- 

 stitial tissue of the testis is derived from the peritoneum, meaning there- 

 by the mesothelium of the genital ridge, I may omit the account of my 

 study of the earlier stages, and proceed to the description of the inter- 

 tubular tissue of the testis in the pig of 23 or 33 mm., a stage imme- 

 diately preceding the appearance of Leydig's cells. 



In the pig of this length the testis may readily be identified, as the 

 rudiments of the tunica albuginea and the mediastinum are fairly dis- 

 tinct, the primitive seminal tubules are well defined, and their basement 

 membrane is formed. The intertubular spaces in the more central por- 

 tions of the gland are, on the whole, larger than those near the periphery. 

 In the latter situation they consist mainly of capillaries derived from 

 vessels of the albuginea, whereas in the former case they are as wide 

 as, or even wider, than the tubules, owing to the presence in considerable 



