356 



DISCOVERY REPORTS 



l cm 



Text-fig. 6. 



Vesicles found in uteri of two 

 pubertal females. 



The corpus luteum of ovulation 



There are records of the diameter of the corpus luteum of ovulation of 59 female fin whales. These 

 are in the recently ovulated class of females, taken in the antarctic, the majority outside the usual 

 conception period for the species (see p. 450). They may be characterized as females which had an 

 apparently normally active corpus luteum in the ovaries, but in which an intensive search of the 

 uterus failed to reveal a foetus. Examination of the mean size of the largest follicle in this group 

 (p. 347) confirms this diagnosis. 



The size range of these corpora lutea of ovulation is 1 "5— 13*5 cm. and the mean diameter, 8-28± 

 0-82 cm., is well below the mean size of the corpora lutea of pregnancy (Text-fig. 7). This corresponds 

 to a mean weight of 0-375 kg. and a weight range of 3-4 g. 

 to 1-5 kg. (Text-fig. 8). Some of these corpora lutea of 

 ovulation are of very recent formation (Text-fig. 5 b) and 

 show the characteristic unexpanded cross-section of an 

 early stage of formation. 



Two of them, which represented first ovulations of 

 females at puberty, were associated with the occurrence 

 of unusual cysts (Text-fig. 6) in the uterine cornu on the 

 same side as the corpus luteum. These cysts were at first 

 thought to be small embryos. They were sectioned by 

 Dr R. Willis (Department of Pathology, The School of 

 Medicine, Leeds), who reported that they do not show any 

 features suggestive of embryonic products or gestational 

 changes. The bulk of the tissue in the walls of the 



vesicles is structureless and degenerate, and where surviving tissue is present it seems clear that it 

 must have arisen from the endometrium itself. 



In its morphology the corpus luteum of ovulation is similar to the corpus luteum of pregnancy and 

 no constant differences have been observed (see below, p. 362). 



The corpus luteum of pregnancy 



Size 



There are insufficient data from the early stages of pregnancy to justify a precise statement about the 

 duration of the initial phase of growth of the corpus luteum of pregnancy. What there is suggests 

 that the corpus luteum continues to grow until the foetus is about 10-20 cm. in length, at an age of 

 one or two months. It then remains of constant size until late pregnancy. The extensive data now 

 available provide no evidence that the corpus luteum decreases in size towards the end of pregnancy, 

 as Mackintosh and Wheeler (1929) suggested. There is actually some slight indication of an increase 

 in corpus luteum size in late pregnancy, because six corpora associated with foetuses averaging 5-74 m. 

 in length were 5 mm. larger in mean diameter than the mean size in earlier stages of pregnancy. 

 Because of the small size of the sample and the variability in corpus luteum size this difference is 

 not significant. 



Chittleborough (1954, p. 46) gives a probable growth curve for the early development of the hump- 

 back-whale corpus luteum by linking the largest corpus luteum found in each month. This suggests 

 that the corpus steadily increases in size for the first two months, when it approaches the range found 

 in late-pregnancy corpora lutea. 



The mean diameter of 523 fin-whale corpora lutea of pregnancy was 11 -44 ±0-154 cm - an ^ the 



