412 DISCOVERY REPORTS 



work, but should be of value if any future observations are made from floating factories, 

 where the genitaha can often be obtained when there is no opportunity of examining 

 the vertebral column. 



When further work has been done on these lines the restriction of comparison to 

 the physically mature whales of successive seasons should lead to a more accurate 

 indication of increase or diminution of stock than is at present available. 



The sexual season is limited in some animals to a single oestrous period, and, ovula- 

 tion taking place at oestrus only, the accumulation of corpora lutea will be slow or rapid 

 according to whether one or more than one ovum is normally shed at this time. In 

 other animals the oestrous (dioestrous) cycle is shorter, and is repeated during the 

 sexual season until pregnancy supervenes or the season ends. In these polyoestrous 

 animals corpora lutea will accumulate rapidly. In some animals again the ovum is not 

 shed unless coition occurs, that is to say, only corpora lutea of pregnancy will be found 

 in the ovaries. 



It is obviously of the utmost importance to discover the condition normally existing 

 among whales if there is to be any solid foundation beneath a theory involving the 

 corpora lutea. 



The reasons for considering Blue and Fin whales as polyoestrous animals in which 

 ovulation occurs regardless of coition are given in the Report (1929) on p. 390. It was 

 there shown that, although foetuses are sometimes lost at sea, and perhaps occasionally 

 very early stages are missed in spite of thorough search, there are too many apparent 

 pregnancies in which no foetus can be found to be accounted for in any way other than 

 by ovulation. 



This view has received support from observations during 1929-30. Thirteen ap- 

 parent ovulations have been noted. The size and condition of the uterus in these whales 

 did not suggest the presence of a foetus, although little reliance can be placed on 

 measurements and observations of congested condition in an organ so capable of rapid 

 recovery as the uterus. When a foetus has been present some indication of the occur- 

 rence can usually be found. During this season three foetuses are known to have been 

 slipped at sea, and one of them, about 0-2 m. long (No. 2753), was discharged in its 

 membranes from the parent whale upon the deck of the catcher that was towing it^. 



Whales have been recorded in which two or more ova have been liberated at the same 

 time, but they are too few to form a serious exception to the rule of normal behaviour, 

 which is the shedding of a single ovum at each ovulation. (See note on Multiple 

 Ovulations on p. 419.) 



That ovulation takes place without the stimulus of coition is now almost beyond 

 doubt. The high percentage of ovulations at South Africa (Saldanha Bay, 1926) and 

 the comparatively large number of ovulations recorded from South Georgia suggest 

 this condition. The only direct evidence is the capture this season of a Fin female with 



1 Whales are towed alongside the catcher tail first and always float ventral side uppermost. Internal 

 decomposition and extra pressure during stormy weather would he sufficient to cause the discharge 

 of the foetus. On the flensing plan foetuses are sometimes blown two or three yards from the parent. 



