THE SPERM WHALE 



129 



whales, though there is very considerable variation for any given length. Few immature 

 Sperm whales have been examined, but the graph shows an increase in size of testis after 

 a length of about 12 m. is reached, which is the length at which sexual maturity is 

 attained. No seasonal variation in size can be traced. 



The histological appearance of the testis in this species is similar to that in the Whale- 

 bone whales, but the tubules in adult whales appear to be always in a greater state of 

 activity than in those species. Only one specimen of inactive testis material is available 

 for examination. This occurs in the testis of an adult whale (No. 1606, 14-9 m. long). 

 Sections show that part of the testis is active and is separated by connective tissue 

 trabeculae from another portion in which the tissue is completely inactive. In the active 

 part the tubules are large, nearly empty, and there is little interstitial tissue. In the other 

 part the tubules are full of cells and there is much interstitial tissue. The cells lining the 



10 12 14 16 



Total Leng'th in metres 



18 



Fig. 36. Sperm whale. Males. Volume of testis plotted against total length. 



tubules of the inactive part appear to be larger than those found in the Whalebone 

 whales, but the large cells filling the tubules are similar (Plate XI, fig. i). Spermatozoa 

 appear to be much more plentiful in the testis of this species than in the Whalebone 

 whales, there being nearly always a fair number to be seen in the tubules of the testis in 

 adult whales (Plate XI, figs. 2 and 3). 



The sexual cycle. Material and observations are available from a series of thirty-six 

 Sperm whales. As described above, the histological details of the testis of the Sperm 

 whale are very similar to those of the Whalebone whales. In examining sections of the 

 testis in the present series the specimens have been classified as active, in which the 

 spermatic tubules are full of cells in various stages of division and have no, or only small, 

 clear spaces in their lumina ; resting, in which the tubules are lined with a comparatively 

 thin layer of cells and have very large spaces occupying nearly the whole of the lumen ; 

 and intermediate, in which there is some activity but the tubules are not packed full of 



