THE TESTICLE AND THE OVARY 367 



by removing one ovary while leaving the other, and by destroying 

 some of the corpora lutea but not all, and in the majority of these 

 cases the animals produced young. The experiments resulted, there- 

 fore, in supporting the view that there is an intimate connection 

 between the presence of the corpus luteum and the occurrence of 

 pregnancy, and that this connection is in a certain sense one of cause 

 and effect. 



Apart from the experimental evidence, Fraenkel adduces certain 

 other facts which tend to support the theory that the corpus luteum 

 is an organ of internal secretion. He points out that its general 

 structure is eminently suggestive of its being a ductless gland, since 

 it is formed mainly of large epitheloid cells surrounded by a network 

 of capillaries and arranged in regular rows or columns not unlike 

 those of the cortex of the supra-renal body. Moreover, the increase 

 in the size of the corpus luteum, until it becomes larger than a 

 Graafian follicle, seems inexplicable on any other view. This unusual 

 capacity for growth is clearly out of all proportion to that of the 

 rest of the ovary, and it is pointed out, further, that when the corpus 

 luteum is most hypersemic, the other part pi the ovary is unusually 

 antemic, while towards the end of pregnancy, when the increase in 

 the blood supply to the generative organs is at its height, the corpus 

 luteum is often reduced to little more than a scar. Fraenkel also 

 lays some stress on the discovery that the luteal cells are derived 

 from the follicular epithelium and not from the connective tissue of 

 the stroma. Furthermore, he observes that whereas many cases have 

 been recorded in which double ovariotomy was performed during 

 pregnancy without interfering with the further course of development, 

 in none of these, so far as he is aware, was the operation conducted 

 in the early weeks. 



Fraenkel observes also that in non-placental Mammals (Marsupials 

 and Monotremes) the corpus luteum is rudimentary or does not exist 

 at all. Sandes,^ who has carefully described the formation of the 

 corpus luteum in the marsupial cat, points out that this is erroneous, 

 and says that there is a large corpus luteum in the members of both 

 these groups. It should be remembered, however, that in Marsupials 

 the embryo is nourished by a " yolk-sac placenta," while in at least 

 one genus (Ferameles) a definite allantoic placenta exists. In Mono- 

 tremes there is a pronounced hypertrophy of the follicular epithelium 

 following upon ovulation, but the corpus luteum is not normal in this 

 group, since there appears to be no ingrowth of connective tissue or 

 blood-vessels from the follicular wall (see p. 143). 



A similar objection, that might be raised in opposition to 

 Fraenkel's hypothesis, is that structures resembling corpora lutea 



' Sandes, lot: ait. 



