ON SOMATIC SEX-CHARACTERS 101 



Somewhat similar processes take place in the ovaries 

 of Teleostean fishes, as I know from my own obser- 

 vations, but no corpora lutea are formed in these, 

 although the degenerating follicles in course of 

 absorption correspond to corpora lutea. The spawn- 

 ing of Fishes, usually annual, corresponds to ovula- 

 tion in Mammals, and in the ovary after spawning the 

 numerous collapsed follicles containing the follicular 

 cells may be seen in all stages of absorption. 1 At 

 other times of the year sections of the ovary show here 

 and there ova which after developing to a certain 

 stage die and undergo absorption with their follicles. 



In the higher Mammals (Eutheria) the corpora 

 lutea show a special relation in their development to 

 the occurrence of pregnancy, that is to say, they 

 have a different history when ovulation is followed 

 by pregnancy to that which they have when the ova, 

 from the escape of which they arise, are not fertilised. 

 When fertilisation occurs the corpus luteum in- 

 creases in size during the first part of the period of 

 gestation (four months, or nearly a half of the whole 

 period in the human species). It then remains 

 without much change till parturition, after which it 

 shrinks and is absorbed. When pregnancy does not 

 occur the corpus luteum is formed, but begins to 

 diminish within ten or twelve days in the human 

 species and is then gradually absorbed. According 

 to O'Donoghue, in the Marsupial Dasyurus there 

 seems to be no difference either in the development 

 of the milk glands or of the corpora lutea between the 

 pregnant and the non-pregnant animal. Sandes 2 



1 Cunningham, 'Ovaries of Teleosteans.' Quart. Journ. Mic. Sci., 

 vol. xl. pt. i., 1897. 



2 Proc. Lin. Soc., New South- Wales, 1903. 



