396 DISCOVERY REPORTS 



whales under 3 hr. post-mortem are rare on factory ships or land stations. The insulating layer of 

 blubber probably accelerates post-mortem changes. Chittleborough has studied the histology of 

 humpback-whale testes from animals in breeding condition, but the material shows signs of post- 

 mortem degenerative changes, with the result that even his material does not present a clear picture 

 of full spermatogenesis (Chittleborough, 19556, PI. 1, fig. 4). In most cases it has been found possible 

 to diagnose a male in full breeding condition or in complete anoestrus, but it is not possible to describe 

 the more gradual histological changes accompanying the approach to or regression from full breeding 

 activity as was possible with well-fixed material collected from seals immediately after death (Laws, 

 1956c). A preliminary examination is sufficient to show that most male fin whales examined in the 



MONTHS 



250 



200 



5 

 < 



150 



IOO 



S AFRICA 



ANTARCTIC 



V 



J A S 



MONTHS 



Text-fig. 28. Annual cycle of testis activity in the male. Above, activity expressed as arbitrary scale of values, based on 

 histological appearance; below, measurements of mean diameters of seminiferous tubules; from Antarctic and South Africa. 



Antarctic are in full anoestrus, but there are some individuals in which the seminiferous tubules present 

 a more active picture. 



Since detailed histological examination and description is not rewarding, a subjective classification 

 into five arbitrary stages of activity has been made using the sectioned material on which Mackintosh 

 and Wheeler (1929) based their account of the male cycle. This includes 86 specimens, mostly from 

 January and February, but including all months except June. On the basis of the overall microscopic 

 appearance the material has been divided into five classes — o, 1, 2, 3 and 4, ranging from complete 

 anoestrus to full activity. The monthly mean according to this scale of values has been calculated and 

 the results are set out in Table 7 and Text-fig. 28. Almost all the pelagic material collected in recent 

 years is from January and February and the great majority of specimens fall into group o as in the 

 earlier material ; it has not, therefore, been included. 



