■ 54 DISCOVERY REPORTS 



extremely rare ; I have never seen one in the course of four winters' work ; and there is 

 no reason to assume that coitus is necessarily fruitful in the lower animals. For example, 

 there is every reason to believe that the stoat copulates during about eight and a half 

 months of the year, whereas the females can become pregnant during only six weeks of 

 the period although they ovulate at other times (Deanesley, 1935), so that sterile inter- 

 course must be frequent. 



In dealing with a wild animal such as Otaria it is obviously impossible to ascertain 

 the length of the oestrous cycle by anything approaching the methods used with labora- 

 tory animals, so that all that can be hoped for is that an estimate of some sort may be 

 arrived at by indirect methods. Of my series 19 were killed in the first three months 

 of the year. The two earliest were both in a very advanced state of oestrus, one of 

 9 January had just ovulated and coitus was observed, the other, of 13 January, contained 

 a very large follicle and had the highest uterine epithelium observed (52^) and coitus 

 was seen. In the second half of January, in February and in March 17 seals were killed 

 and they were all in a state of post-ovulation activity, pseudopregnancy or very early 

 pregnancy, which are indistinguishable states, unless blastocysts are found. From June 

 to September the seals killed include both oestrous and post-ovulation animals, although 

 the former are in the majority. But this may have been due to the relative ease with 

 which non-pregnant animals are picked out if they are attended by bulls, who would 

 naturally be more attached to oestrous than to post-ovulation cows. In December, that 

 is, in the earlier part of the breeding season proper, eleven cows were killed, all in 

 oestrus. It may be tentatively suggested that although cows come on heat very rapidly 

 indeed after parturition (e.g. no. 531, p. 145), the succeeding stages of pseudopregnancy, 

 when fertilization has not taken place, extend over some weeks, and this does not seem 

 unreasonable when the length of pregnancy is considered (1934, p. 300). That the species 

 is polyoestrous is shown by the overlapping of the last stages of the post-ovulation 

 condition with the earlier stages of oestrus, e.g. nos. 465 and 457, which display mitoses 

 etc. in the uterine epithelium as well as some glandular activity. 



I have killed specimens in oestrus or post-ovulation stages in every month except 

 April and May. There are no animals from April and those of May are unfortunately 

 all pregnant. The two October cows were very large animals with massive uteri which 

 contained many hyalinized blood vessels ; their follicles were all less than 07 cm. in 

 diameter, but each had a well-developed corpus luteum. There were no mitoses in the 

 uterine epithelium and the glands were rather active. I consider that these animals 

 are in a pseudopregnant condition which is masked by the signs of senility indicated 

 above. 



It appears then that in spite of the occurrence of a quite well-defined breeding season 

 there is no division of the year into oestrous and anoestrous periods. On the contrary, 

 Otaria, as a species, is sexually active all the year round. 



Since neither sex has periods of functional sterility the reason for the contraction of 

 the breeding periods into a comparatively short time in summer is obscure. The neces- 

 sity of suckling a pup cannot be a controlling factor, since both lactating and non-lactating 



