308 Dr Doncaster, A possible connexion between 
In the paper referred to, I mentioned that I had in my 
possession a tortoiseshell tom, which I was mating with black 
females in the hope of testing this hypothesis. The experiment 
has now been in progress for about nine months; the tom has 
mated, apparently successfully, with each of four females several 
times, but none of them have become pregnant. (The females 
have had respectively two, three, five and five periods of ‘heat’ 
during the time, and at each period there have been one or more 
apparently normal copulations.) 
It seems fairly clear, therefore, since three of the four females 
have previously borne kittens to other sires, that the tom-cat 
is sterile. This is confirmed by facts pointed out to me by Dr 
F. H. A. Marshall. On examining one of the females about four 
weeks after the last pairing, he found that the mammae were 
swollen and on pressure exuded a small amount of milk. This 
continued for about two weeks, after which the exudation became 
less and finally disappeared. Now it is known that there may be 
correlation between the development of corpora lutea and mam- 
mary hypertrophy, and Marshall and Hammond have found that 
in rabbits from which the uterus has been excised so that preg- 
nancy is impossible, slight lactation may supervene after ovulation, — 
* 
| a oe 
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i eee 
owing, apparently, to the presence of corpora lutea in the ovary, — 
and that a period of ‘heat’ does not recur until this lactation has 
ceased. Further, Longley* has shown that in the cat ovulation 
only occurs after copulation. If, then, the slight lactation ob- 
served was caused, as in the rabbit, by the presence of corpora 
lutea consequent on ovulation, the copulation must have been 
sufficiently normal to cause ovulation, which does not take place 
in its absence. That ovulation occurred is also suggested by the 
rather widely separated periods of heat. Cats in the breeding 
season usually come on heat every three weeks or oftener; my 
females, after pairing with the tortoiseshell tom, did not come on 
again as a rule for at least five weeks, and usually not for six — 
weeks or even more. When all these facts are taken together, 
there seems to be little doubt that the tom is sterile, although he 
1S monmiely formed and has the sexual instincts strongly developed. 
If this were an isolated case, it might be of no importance, but 
there are hardly any records of offspring of tortoiseshell males, and 
the few that exist are perhaps not wholly above suspicion. I 
believe that two such cats at least are well known never to have 
become parents, and I know of another case in addition in which a 
tortoiseshell tom was paired but no pregnancy followed. It seems, 
therefore, that the abnormal constitution of a tortoiseshell tom 
with regard to its inherited characters may be connected with 
* W. H. Longley, ‘‘ Maturation of the Ege and Ovnlations in the Domestic Cat.” 
Amer. Journ. Anat. x11. 1911, p. 139. 
