THE REPRODUCTIVE CYCLE 399 



eleven humpback whales taken in February which is higher than that for Chittleborough's sample. 

 In fact the maximum diameter they found was 290 11 which seems very high, but their sections were 

 cut from frozen material without embedding, so the shrinkage would be expected to be much less 

 than in paraffin-embedded material. We are comparing here anoestrous fin and humpback whales with 

 humpback whales in rut and one would expect the latter to show much higher values with identical 

 treatment. 



In pinnipeds of at least four widely different genera the tubule diameters in rut are about 220 11 and 

 shrink to less than 140^ in anoestrus (Laws, 1956c, fig. 7; McLaren, 1958, fig. 3; Mansfield, 1958, 

 fig. 15). The antarctic fin-whale material suggests that there is a similar range in whales. In this 

 material anoestrous tubules are about 140// in diameter (Text-fig. 28) and the largest measured 

 (241 11) was either approaching rut or taken immediately after. 



250 



200 



150 



100 



510 15 2005 O 

 FREQUENCY 



IO 15 20 



Text-fig. 29. Measurements of seminiferous tubules. A, humpback whale, West Australia; B, fin whale, South Africa; 

 C, fin whale, antarctic; D, E, and F, means ± 20- and s.e. for antarctic fin whales classified as to diatom infection; D, recent 

 arrivals; E, heavy diatom infection, South Georgia; F, heavy infection, antarctic pelagic. 



It seems probable then that the fin-whale material from South Africa and the humpback-whale 

 material from Australia has undergone much greater shrinkage than the antarctic material, so that 

 the testis tubule diameters cannot be directly compared. It is also possible, however, that the South 

 African material gives a true picture, relative to the antarctic material, and that there is a decrease 

 in average tubule diameter from July to September, followed by an enlargement associated with the 

 southward migration. This possibility is discussed later (p. 453). It seems clear, when the evidence 

 is combined, that there is a very definite cycle of activity in the male fin whale. It should be noted 

 that the bulk of the fin-whale population is in the Antarctic during the months covered by the samples 

 because at this time they must feed in antarctic waters (Mackintosh and Brown, 1956, fig. 2; Marr, 

 1956). It can safely be assumed that, so far as it goes, the material gives a true picture of the male 

 sexual cycle. 



The individual rate of regression in tubule diameter is actually greater than Text-fig. 28 suggests, 

 because of the smoothing effect of the continued arrival in the Antarctic of males from lower latitudes. 

 Even in January and February there are some males with seminiferous tubules about 200 p in mean 

 diameter and it seems likely that these are recent arrivals. Is there any way of confirming this? Hart 

 (1935) showed that the presence of a thick diatom film on the surface of the body can be taken to 

 indicate that a whale has been in antarctic waters for at least a month, and conversely, the absence 



