232 DISCOVERY REPORTS 



The possibility of clerical error in recording the data in connection with this 1935-6 

 sample must not be overlooked for reasons which are dealt with in the next section, 

 where the entire collection is considered in detail. It is probably safe to conclude that 

 this larger sample has nothing to show which conflicts with the results of personal 

 examination of other material. 



incidence of pregnancy. It has been found that the most reliable guide to the 

 percentage of adult whales pregnant is the presence or absence of a corpus luteum of 

 pregnancy on the ovaries. Direct comparison has been made between the number of 

 foetuses reported in the ship's whaling log and the number of pregnancies evidenced by 

 the presence of corpora lutea of pregnancy on a sample of ovaries from the same ship. 

 A higher percentage of pregnancy is indicated by the ovaries than by the log. There are 

 two reasons for this discrepancy. Small foetuses tend to be missed, because on whaling 

 ships operating under normal conditions time does not permit a careful search for 

 foetuses. Only when a foetus is plainly to be seen on dismemberment of the mother will 

 a record be made of it. Further, visibility on deck at night is poor, and, though flood- 

 lights suffice for general work, they are not strong enough to show up a foetus among the 

 welter of meat, bones, and entrails which is inseparable from work on the congested deck 

 of a factory ship. The discrepancy is of some importance, since it involves the calculation 

 of fertility among adult Blue females. Further remarks will be made on this subject in 

 the section on the rate of breeding. 



I examined the ovaries of 180 whales on board the ' Southern Princess', and of these 

 ninety-six showed the corpus luteum of pregnancy and were accompanied by a foetus. 

 Four whales showed a functional corpus luteum, but no accompanying foetus was found 

 nor did the condition of the uterus indicate that the whale was pregnant. These whales 

 may be regarded as having quite recently ovulated; the corpus luteum was probably 

 that of "pseudo-pregnancy". A small number of whales ovulating during the summer 

 has been noted by Mackintosh and Wheeler among the whales examined at South 

 Georgia (p. 390). In estimating the percentage of pregnancy among adults simply from 

 a study of the ovaries it will be necessary to allow for those functional corpora lutea 

 which may have been those of pseudo-pregnancy. There is no means of telling whether 

 the number of ovulating whales recorded above represents a constant proportion of the 

 total adult females. The most profitable way to treat the matter is probably to assume 

 that the incidence of apparent pregnancy among whales from which the only evidence is 

 that of the ovaries, as in material considered below, is slightly too high, and that the 

 figure is a maximal one to be used with caution. 



foetal sex ratio. 206 foetuses were measured by myself or the foreman in charge 

 during the night. The sexes were represented as follows: 



Male 112 or 54-4% 



Female 94 or 45-6% 



A slight preponderance of males over females is observed here and confirmed by records 



