142 MAMMALIAN SEXUAL CHARACTERS 



diffusing from the ovum during its development in 

 the uterus would continue to stimulate the follicle 

 cells, and thus explain not merely their persistence, 

 but their secretory activity. The ovum being no 

 longer present in the ovary, the secretions would 

 remain in the follicular cells, and the corpus luteum 

 would be explained. 



If this theory is sound, it would follow that corpora 

 lutea are not formed in cases where the ova are not 

 retained in the oviduct during their development. 

 The essential process in the development of these 

 structures is the hypertrophy and, in some cases at 

 least, multiplication of the follicular cells in the 

 ruptured follicle. I have already mentioned that 

 this process does not occur in Teleosteans whose 

 ovaries were studied by me. These were species 

 of Teleosteans in which fertilisation is external. 

 Marshall, in his Physiology of Reproduction,^ quotes 

 a number of authors who have published observations 

 on the changes occurring in the ruptured follicle in 

 the lower Vertebrata, and also in the Monotremes. 

 According to Sandes,^ in the latter there is a pro- 

 nounced hypertrophy of the follicular epithelium 

 after ovulation, but no ingrowth of connective 

 tissue or blood-vessels from the follicular wall. 

 Marshall himself examined sections of the corpus 

 luteum of Ornithorhynchus and saw much hyper- 

 trophied and apparently fully developed luteal 

 cells, but no trace of any ingrowth from the wall of 

 the follicle. This fact would appear to be quite 

 inconsistent with the theory above proposed, but 



1 London, 1910, p. 151. 



2 'The Corpus Luteum of Dasyurus,' Proc. Lin. Soc, New South 

 Wales, 1903. 



