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Ovulation and Degeneration of Ova in the Rabbit. 
By WatLter Hearse, M.A., Trinity College, Cambridge. 
{Communicated by Adam Sedgwick, F.R.S. Received March 6,—Read April 6, 
1905.) 
It has long been held that ovulation invariably occurs in all animals at each 
period of cestrus. 
I have already shown (Nos. 13, 14, 15) that this is not necessarily true for 
menstruating animals. In other polycestrous animals also there seems reason 
to believe that when coition is prevented during the first few recurrent cestrous 
periods, ovulation is interfered with during the subsequent periods, for 
conception is then much more uncertain than it is if coition oceurs when the 
sexual season first appears. | 
Moreover, among bats there is clear evidence that ovulation does not 
necessarily occur during cestrus (Nos. 2, 4, 5, 8), for the mature females are 
impregnated in the autumn and do not ovulate until later, probably the 
following spring; although the young females, born in the late spring, do not 
copulate until the spring of the following year at the time when ovulation 
also occurs. : 
With these facts before me I began, in 1894, investigations on the domestic 
rabbit. Over one hundred does were experimented on, and being kept in 
locked cages, of which I only had the key, certain errors so common with 
breeding experiments were avoided. The ovaries were preserved in various 
ways, and the histological results here given are determined from serial 
sections of which I have some 120 series. 
It was found that the domestic rabbit does not ovulate until, approximately, 
10 hours after copulation (cf Nos. 1,3). The doe rabbit only permits coition 
when undergoing cestrus, and if the male is withheld at that time the ripe 
ova in the ovary degenerate; they are not dehisced from the ovary. Neither 
stimulation of the vulva with electrodes, nor artificial insemination, nor 
subcutaneous injection of spermatozoa induced ovulation ; moreover ovulation 
did not follow coition if from any cause a sufficient supply of blood to the 
ovaries was interfered with; while at the same time, provided this supply of 
blood was not interfered with, artificial stoppage of the progress of the 
spermatozoa from the vagina did not interfere with ovulation. 
The Graafian Follicle and Ovum.—the follicle consists of a thick layer of 
epithelium, bounded on its outer edge by a basement membrane. Within, 
the ovum lies surrounded by its zona radiata. The structure is embedded in 
