212 INTERNAL SECRETIONS 



lutein pigment in these cells the different authors disagree. 

 The cells are smaller than those of the corpus luteum {Figs. 

 94, 97). According to Limon (1901) these cells occupy in the 

 bat and in the mole almost the whole ovary forming a paren- 

 chyma traversed only by blood vessels. The same is true for 

 the rabbit, as seen in Fig. 98. 



Interstitial cells may be found in the ovary already during 

 embryonic life. 



As mentioned above, most authors, especially Winiwarter, 

 insisted that interstitial cells are present in the ovaries of 

 all species. Fraenkel (1905) and Schaeffer (1911), who studied 



A ^ 



Fig. 94. — Ovary of rabbit 18 months old (Prot. Nr. 44). Fix. in the solution of 

 Helly. A, Cells of Corpus luteum; B, Interstitial cells. The cells of the 

 C.l. are bigger; the protoplasm of both is highly vacuolated. The cells 

 are associated with closed capillaries. — Prepar. of Wagner; design of 

 Lehbert. 



a great number of different species, concluded, on the contrary, 

 that these cells are not always present in the ovary. But 

 their material was very incomplete for many species, only one 

 or a few ovaries having been investigated. Since the 

 interstitial cells are not to be found always in different indi- 

 viduals of the same species, the absence of interstitial cells 

 in one or some individuals of a given species is not sufficient 

 evidence for concluding that these cells are really absent in 

 that species. The interstitial cells in the ovary vary, indeed, 

 very greatly in number and size, according to age. Anyone who 

 examines a sufhcient number of ovaries of the rabbit will confirm 

 this {Fig, 99 A, B, C). The interstitial cells which are always 

 present in the adult rabbit do not acquire the size characteristic 

 of the adult animal until about the age of six months. Up 



