23» 



DISCOVERY REPORTS 



the length at which the onset of physical maturity begins to limit the growth of some 

 but not all Blue females is found, and from a deeper analysis it appears that up to the 

 time of physical maturity there is some relation between length and the average number 

 of corpora lutea. This relation will be further inspected when we deal with the larger 

 collections of ovaries gathered in 1934-6. 



It should be mentioned that the foregoing argument is confined solely to the material 

 which I collected personally in 1932-3. Unfortunately the material collected subse- 

 quently, while satisfactory in other respects, contains no records of the degree of 

 physical maturity of the whales from which the ovaries were taken. 



20- 



< 



UJ 



2«5 



o 



Q. 

 O 



u 



o 



10 



5- 











80 65 30 



LENGTH OFWHALE IN FEET 



95 



Fig. 6. Lengths of physically immature and mature whales (1932-3). 

 (Pecked line, immature; solid line, mature.) 



summary, i. Blue females taken in pelagic whaling appear to attain sexual maturity 

 on the average at the same length (78 ft.) as South Georgian whales. 



2. The presence of a corpus luteum of pregnancy in the ovaries is taken to be the 

 best index of pregnancy of the animal though some allowance must be made for whales 

 ovulating in the summer and exhibiting a corpus luteum of ovulation, or pseudo- 

 pregnancy. 



3. A slight predominance of males is found in foetuses, in agreement with the foetal 

 figures in International Whaling Statistics. Males are about 54 per cent of the total and 

 females about 46 per cent. 



4. The foetal growth curve as indicated by the mean monthly lengths of foetuses 

 agrees closely with the mean growth curve for Blue whales taken in South Georgia. This 

 is a strong indication that the Blue whales in both regions are essentially similar in their 

 breeding habits and observe the same mean pairing season. 



5. Frequencies of corpora lutea numbers in Blue whales do not show the maxima 

 and minima on which a deduction of age was made for Fin whales. 



