THE REPRODUCTIVE CYCLE 397 



Smears of testes and epididymides from 17 mature fin whales were examined by A. H. Laurie 

 and F. D. Ommanney at Durban, South Africa (unpublished work). This material was collected in 

 June, July and August and spermatozoa were present in all except two specimens. 



Table 7. Arbitrary classification of testis samples according to activity 



Arbitrary classification 



* , Arbitrary 



1234 mean 



3 2 0-4 



2 — 0-2 



I — 2 



I — 2-2 



1] 



4-oj 



1 3-0 



4 2'0 



2 2 I 1-8 



2 — — — 07 



3 2 1-4 

 2 1 — 1-3 



13 12 8 3 



From this examination it appears that the period of maximum testicular activity extends from about 

 April to July or August with peak activity probably in May and June, and it is at a minimum in 

 January and February. Owing to the scarcity of material from March to October it is not possible 

 to say more than this. 



Variations in the diameter of the seminiferous tubules 



Individuals of many species of mammals show a seasonal cycle in the diameter of the seminiferous 

 tubules, correlated with histological changes in the contents of the tubules (Laws, 1956c). The 

 seminiferous tubules are narrow in anoestrus, enlarge just before the breeding season and shrink again 

 afterwards. Whales might be expected to show a similar cycle of growth and regression, but the full 

 extent of these changes appears to be masked by the amount of chronological variation in the indivi- 

 dual cycles. Chittleborough (19550) for instance, could demonstrate no change in testis weight or in 

 the diameter of the seminiferous tubules of humpback whales taken over a period of 4I months from 

 June to October, but Omura (1953) and Symons and Weston (1958) found the testis weight to be lower 

 in antarctic specimens than those in Chittleborough's sample. These authors also state that the testes 

 of humpback whales taken in February present an inactive appearance when examined histologically. 



As explained above, whale testis material is often badly fixed and shows degenerative changes. In 

 measuring the diameter of the seminiferous tubules only material which showed no obvious shrinkage 

 of the tubules has been accepted. This limits the material to samples from 95 mature male fin whales, 

 the histological appearance of the tubule contents being the criterion of maturity adopted. As the 

 testis of males approaching puberty probably presents an appearance similar to that in inactive 

 mature males, it is possible that some immature males have been included inadvertently, but these are 

 unlikely to have much effect on the general conclusions. 



For each of these 95 whales the mean tubule diameter was calculated from a random sample of 

 20 tubules, except for a small minority in which only 10-15 were measured. Measurements were 

 made with a graduated scale on projected histological sections and only roughly circular tubule 

 sections were measured across two diameters at right angles ; this helped to make the samples random 

 and ensured that the full tubule diameter was measured. 



