398 DISCOVERY REPORTS 



Table 8. Summary of records of the diameter of seminiferous tubules of 

 antarctic male fin zvhales by months 



The results are shown in Text-figs. 28 and 29 and summarized in Table 8. Taking first the antarctic 

 samples it will be seen that, although there is a wide range of variation in tubule diameters, the monthly 

 mean value progressively declines from 164// in October to 140// in February. This continued 

 decrease in the tubule diameter strongly suggests that the testes of male fin whales taken in the 

 Antarctic from October to February are regressing following a season of activity at an earlier period. 

 Clarke (1956) found a closely similar decrease in monthly mean tubule diameters in male sperm whales 

 taken in the vicinity of the Azores (from 161 // in June to 134/^ in September and 144 fi in October). 



After February there is apparently an increase in the tubule diameters. The monthly mean for 

 March is 208 fi, but this is probably too high, being the average of only two whales, and probably over- 

 influenced by the high value for one of them (tubule diameter 241 //, the largest tubule diameter 

 measured). The lower of these two values (tubule diameter 175 //) was from a specimen in which the 

 tubules were in early spermatogenesis and, therefore, probably enlarging prior to the breeding season. 

 The other specimen had a number of degenerating spermatids in the lumen and may have been either 

 approaching rut, or immediately post-rut. An observation of the extent of diatom infection might 

 have helped to place this very interesting animal (see below), but unfortunately no notes were made 

 on this point in the field. If the seven specimens for March, April, and May are taken together they 

 suggest a mean diameter of about 165 /i in April. 



Turning now to the testis tubule diameters for the eight mature males from Saldanha Bay, South 

 Africa, taken in July, August and September (Text-fig. 28) it will be observed that only two have 

 tubules above 140 ju in diameter, which is very much lower than expected. These few specimens 

 suggest a possible decline in tubule diameter over this period but the August and September means 

 are below the lowest monthly mean values in the antarctic samples. Referring again to the arbitrary 

 scale of testis activity based on the histological appearance of the seminiferous epithelium it will be 

 seen that these testes from July, August, and September are more active than those from later months. 

 The most probable explanation of the discrepancy is that the post-mortem and post-fixation treatment 

 has been different, and has produced greater shrinkage in the South African material. It will, how- 

 ever, be remembered that only fin-whale material showing no obvious shrinkage has been used. It is 

 relevant to note that the frequency distribution of humpback-whale tubule diameters, measured by 

 Chittleborough (1955a, fig. 10), is almost the same as that for fin whales. These are compared in 

 Text-fig. 29 A and C, and it will be noticed that two fin-whale values are higher than the highest value 

 for humpback whales. The present material was Bouin-fixed or formol-saline fixed whereas Chittle- 

 borough's material was fixed in Susa or formol-saline. The different fixation should not in itself 

 produce very marked differences in shrinkage, and most shrinkage occurs in pre-embedding prepara- 

 tions (Baker, 1958). Symons and Weston (1958) also give a mean tubule diameter for a sample of 



