26 THE SEX-COMPLEX 



The develop- the degree of fixity of the ovum in the uterus, one would 



c^pus° f * 6 expect to find that the higher the animal in the scale of 



luteum not evo lution the more important has become the corpus 



the degree of luteum — that in Woman this structure is more active 



ovum.° e than in the rabbit and other lower mammals. Evolution, 



however, does not necessarily entail the advancement of 



every structure; some atrophy, and all are dependent for 



their development upon the necessities of the particular 



species. In the human subject, in carnivora and in 



rodents there is an actual embedding of the ovum ; 



but in ungulates the placental attachment is one of 



apposition, and there is no invasion of the maternal 



tissues as in rodents, carnivora, the primates and Man. 



Moreover, the corpus luteum of an ungulate has a very 



active appearance, both macroscopical (fig. 7) and 



microscopical (fig. 8). Probably, however, the uterine 



mucosa requires as much preparation for placental 



apposition as for trophoblastic digestion. 



Such facts are bewildering ; so the conclusion we must 

 draw provisionally is, that, if the corpus luteum be an 

 organ of internal secretion which assists the implantation 

 of the ovum, the importance of it varies in different 

 species, and probably it has more than one function 1 . 

 I have dwelt on the difficulties of investigating 

 the morphophysiology of the corpus luteum, for we 

 encounter the same difficulties and obtain the same 

 variability in our results throughout this subject of the 

 Sex- Complex in our search after definite information. 

 The inter- j ne interstitial cells of the ovary, also, have attracted 



stitial cells of . . 



the ovary. much attention, and they, too, are believed to possess a 

 special internal secretion. Limon 2 first called attention 

 to la glande interstitielle de Vovaire, as he termed it. 

 Fraenkel 3 , also, has investigated this subject carefully. 

 He compared the ovaries of forty-five different species of 

 mammals, and found an enormous difference in the pre- 

 ponderance of interstitial cells in the various organs. 



1 See also p. 31. * , 



2 Limon, M., Archiv. d. Anat. Micros., 1902-3, vol. v, p. 155 



3 Fraenkel, L., Archiv. /. Gynak., 1905, vol. Ixxv, p, 443. 



