390 DISCOVERY REPORTS 



recorded in February among twenty mature whales taken in this month, two in March 

 among thirty-six mature whales, one in May from among four adults, and one in 

 October among seven adults. At Saldanha Bay there were three such corpora lutea 

 in June among six mature females, and one in July among five adults. Early foetuses 

 were found in July and August. Thus in the case of Blue whales also ovulation takes 

 place to the greatest extent during the southern winter. 



It is not known for certain whether ovulation takes place spontaneously, but there 

 is evidence besides that furnished by the corpora lutea of ovulation to show that the 

 ovum is shed at oestrus whether coition occurs or not. The corpora lutea simply show 

 that fertilization of the ovum probably does not always occur, but this does not neces- 

 sarily mean that copulation had not taken place. In a Fin whale (No. 76) of 20-2 m., 

 the "vaginal band" was found intact, showing that coition almost certainly had not 

 taken place. A small body like an old corpus luteum was however found in one of the 

 ovaries which otherwise appeared to be immature. Luteal tissue was present in this 

 structure surrounding a tough capsule with viscid contents. It is to be supposed that 

 the follicle had matured early (the whale was captured at South Georgia in March) 

 and formed a corpus luteum of ovulation following spontaneous rupture. The condition 

 of the corpus luteum appears to have been abnormal, and it is not entirely certain that 

 an ovum was actually shed, but the formation of luteal tissue shows that the follicle 

 had at least attained a size ripe for shedding. 



(e) The Corpus Luteum subsequent to Parturition 



It is reasonably certain that ovulation does not normally take place after pregnancy 

 until the end of lactation. Among all the whales examined no lactating whale was 

 pregnant or showed any indication of ovulation. There have been reports of lactating 

 whales which were pregnant (see Hinton, pp. 97 and 98), and one may suppose that 

 though ovulation and fertilization may possibly occur during lactation, such an 

 occurrence is extremely rare. 



In the ovaries of whales captured during lactation there are normally several old 

 corpora lutea, one of which is still conspicuously bigger than the others (Plate XLI, 

 fig. i). This is the former corpus luteum of pregnancy persisting after the birth of 

 the foetus. It is much smaller and tougher than it was during gestation and the change 

 appears to have taken place comparatively abruptly. In Fin whales the size varies 

 from 4 cm. to 8 cm. diameter, with an average of 5-3 cm. In Blue whales the average is 

 7-0 cm. diameter. The changes in size and consistency are due to shrinkage of the 

 luteal cells and growth of the connective tissue which take place rapidly after parturition. 

 Sections of these corpora lutea stain faintly and generally with Nile Blue. 



It remains now to consider the old corpora lutea which are often present in con- 

 siderable numbers in the ovaries, and in various stages of degeneration (Plate XLI, 

 figs. 2 and 3). More than one functional corpus luteum (i.e. corpus luteum of ovulation 

 or of pregnancy) has never been known to occur at one time in the ovaries, but over 

 thirty old corpora lutea have sometimes been counted in the two ovaries together. 



