1905.] the Interstitial Cells of the Ovary in the Rabbit. 



43 



whose condition happens to have been best, and will, therefore, survive in 

 the struggle for existence. 



This cannibalism on the part of the young ovum is not surprising, if the 

 life of an ovum be considered. It is really but the normal condition of 

 the cell at all its stages of development ; it grows and fattens at the expense 

 of other cells. In the young ovary it is starting its first stage of growth 

 and must devour other cells ; later on, when it grows duriug the growth 

 of the follicle, it lives upon the follicle cells, and later still, when, after 

 fertilisation, the ovum in its extended sense refers to the young foetus, it 

 lives on the material provided by the cells of the maternal organism. 



This massing of cells and subsequent demolition of some of them for the 

 benefit of one will be again dealt with in connection with the ovary of the 

 pregnant rabbit. 



Changes in the Ovary during Pregnancy. 



The young ovary, after the period when it has reached a stage where the 

 general aspect is that of an adult ovary, enters upon a period of slow 

 growth, during which there is a continual formation of a considerable number 

 of follicles, which having reached a state of partial maturity then begin to 

 atrophy and finally disappear, leaving only a faint trace of their former 

 existence in the shape of a scar. 



Having reached sexual maturity, the ovary becomes subject to periodic 

 influences, of the nature of which little, if anything, is known. According 

 to Fraenckel (9), they are intimately connected with the hypertrophy of the 

 mucous membrane of the uterus. The sum total of the influences at work 

 results in the production of " heat," which occurs in the rabbit about once 

 a fortnight, but the external changes in the vulva by which this is judged 

 take place very gradually, so much so, that in the spring and summer time, 

 when breeding is most prolific, the adult rabbit is scarcely ever out of one 

 or other stage of " heat." It is fairly certain, therefore, that whatever 

 changes may take place in the ovary during " heat," the condition recurs too 

 frequently for these to be very marked. This does not refer in any way 

 to the formation of the corpora lutea of " heat," which are, of course, very 

 definite. It has recently been stated by Heape (10) that unless impregna- 

 tion occurs the ripe follicles of " heat " do not burst, in which case, 

 presumably, there can be no formation of corpora lutea. If this is the case 

 it would seem that there can be no such thing as the corpus luteum of 

 " heat," and the changes in the ovary during this period must be considered 

 to consist merely of those taking place before sexual maturity, only rather 

 more marked, namely, the formation of follicles, but after puberty these 



