THE REPRODUCTIVE ORGANS 389 



in pregnant ovaries are those that would later have discharged their ova had not 

 fertilization occurred. During lactation the larger follicles, having apparently attained 

 a size that is beyond retrogression, remain large but lose the turgidity they had before 

 and during pregnancy, while the smaller follicles retrogress to become again hidden 

 beneath the surface of the ovary. 



{d) The Corpus Luteum of Ovulation 



In certain whales no foetus was found in the uterus yet a corpus luteum similar to 

 the corpus luteum of pregnancy was present in the ovaries. Assuming that no foetus 

 was missed in these cases, it may be said that these were corpora lutea of ovulation, 

 i.e. representing an ovum which had been shed quite recently. There are, in such 

 circumstances, two occasions on which a foetus may be missed. It may be lost at sea 

 through premature birth when the whale is killed, or it may be so minute that it cannot 

 be found. The former could hardly occur except when the foetus is fully large enough 

 to leave unmistakable evidence of its presence in the uterus. There have in fact been 

 two clear cases in which it has occurred, for in No. 373 (Fin) and No. 1602 (Sei), 

 although no foetus was present, some of the membranes were still in the uterus, and 

 even had these been lost the swelling and congestion of one cornu of the uterus could 

 not have been missed. With regard to the second possibility it may be said that the 

 smallest foetus can hardly be missed if searched for in the proper manner. When a 

 functional corpus luteum is present in the ovaries the uterus is at once spread out and 

 slit open from end to end. The foetal membranes of even a 2 mm. embryo form an 

 object about the size of a thrush's egg and can readily be seen. It may be said then 

 that those functional corpora lutea which were not found to be accompanied by a 

 foetus, were corpora lutea of ovulation or were accompanied by a foetus not exceeding 

 I or 2 mm. in length. It is in any case certain that in all the whales in question 

 ovulation had occurred relatively very recently. Of these whales there were nine Blue 

 and four Fin whales. None had any sign of a foetus and the copora lutea were on the 

 average smaller than the corpus luteum of pregnancy except in No. 250 (Blue) in 

 which the corpus luteum had a mean diameter of 14-7 cm. This contained an enormous 

 cavity and was obviously a very young structure. 



Corpora lutea of ovulation in Fin whales occurred at South Georgia once in February 

 among fifty-two mature females, and at Saldanha Bay once in June (the only adult 

 female), once in July (also the only adult female) and once in September (among three 

 mature females). Very small embryos were found twice at South Georgia in January 

 (one in 1926 and one in 1927) and once at Saldanha Bay in the only mature female 

 taken in August. Now only 8 per cent of the female Fin whales taken at Saldanha Bay 

 were adult, whereas at South Georgia over 60 per cent were adult. Thus the ratio of 

 ovulating females to other mature females is overwhelmingly greater at Saldanha Bay 

 than at South Georgia. That is to say, a far greater percentage of Fin whales are 

 ovulating during the southern winter than during the southern summer. 



Among Blue whales again at South Georgia one corpus luteum of ovulation was 



