366 THE PHYSIOLOGY OF REPRODUCTION 



does not recur until after an anoestrous period, which is often of 

 considerable duration, and that it is extremely improbable that 

 ovulation occurs during this period. 



Beard's theory has been adopted by Sandes, 1 who investigated the 

 corpus luteum of the marsupial cat (Dasyurus viverrinus, see p. 142). 

 This author states that in Dasyurus, as in most other Mammals, the 

 corpus luteum disappears towards the end of the lactation period, 

 when the next osstrus is approaching, and the follicles are beginning 

 to grow in preparation for the ensuing ovulation. He says, further, 

 that as soon as the corpus luteum is formed, the ova in the 

 surrounding follicles, which were up to that time in various stages 

 of active development, begin to undergo atrophy. This atrophy 

 commences in the follicles in closest proximity to the newly formed 

 corpus luteum, and is continued in the surrounding follicles in ever- 

 widening circles. Sandes suggests that this result is brought about 

 by mechanical pressure, or is due to the internal secretion of the 

 corpus luteum, if it has one. Without in any way disputing the 

 accuracy of the facts which Sandes describes, it is difficult to under- 

 stand what advantage is gained by a mechanism having a not more 

 important object than that of securing the degeneration of the surplus 

 ova within the ovary instead of externally to it, and it is not easy to 

 see how, according to the usually accepted doctrines of utility and 

 natural selection, an organ having such a purposeless function could 

 ever have been developed at all. 2 



Gustav Born was the first to suggest that the function of the 

 corpus luteum might be to provide an internal secretion which 

 assisted in the attachment of the embryo to the uterine mucosa. 

 Unable to undertake the investigation himself, he persuaded Ludwig 

 Fraenkel 3 to put his theory to an experimental test. For this purpose 

 a series of experiments upon rabbits was proceeded with, the ovaries 

 being removed at intervals varying from one to six days after the 

 occurrence of coition, the period of gestation in this animal being 

 thirty days. The rabbits were afterwards killed, when it was found 

 that the extirpation of the ovaries had prevented the fixation of the 

 embryos, or had caused these to be aborted. In other cases the 

 corpora lutea are described as having been burnt out by the electric 

 cautery without destroying the rest of the ovaries, and these experi- 

 ments led to a similar result. Control experiments were performed 



1 Sandes, "The Corpus Luteum of Dasyurus viverrinus" Proc. Linnenn <S'or., 

 New South Wales, vol. xxviii., 1903. 



2 Pearl and Surface state that extract of corpus luteum of cow injected into 

 a laying fowl inhibits ovulatipn. ("Studies on the Physiology of Reproduction 

 in the Domestic Fowl," IX., Jour. Diol. Chem., vol. xix., 1914.) 



3 Fraenkel and Cohn, " Experimentelle Untersuchungen iiber den Einfluss 

 des Corpus Luteum auf die Insertion des Eies," Anat. Am., vol. xx., 1901 ; 

 Fraenkel, loc. fit. 



