BREEDING AND LIFE CYCLE 263 



The volumes of both testes were measured in each of 124 whales during 1949 and from 1952 to 

 1954. For fifty-five whales the field-notes distinguish the left from the right testis, and there seems to 

 be'a tendency for the left testis to be the larger: in thirty-three whales the left was the larger, in seven- 

 teen both testes were the same size, and in five the right was the larger. Nishiwaki (1955, p. 147) also 

 found that in sperm whales from the Antarctic the left testis was usually heavier than the right, 

 although Nishiwaki & Hibiya (195 1, p. 161) say that in sperm whales captured off Japan either side 

 of the animal may have the heavier testis. 



In Fig. 4, where testis size is plotted against body length of the Azores whales, the volumes of both 

 testes have been added together. It is unfortunate that data are so few for whales between 8-o and 

 9-5 m. because the trend of the points suggests that this range may be critical ; but it does appear from 



» * . 



20 



10 



IO II 12 13 14 15 16 17 18 



Length in metres 



Fig. 4. Males. Length of body and total volume of testes in whales examined at Horta in 1949 and 1952-4. 



the diagram that by the time most whales have reached a length greater than about 9-5 m. a significant 

 increase in the size of the testis has begun. 



Material from ninety-three whales, collected in 1949, 1953 and 1954, has also been examined 

 histologically, because, as Mackintosh (1942, p. 219) has pointed out, histological examination is the 

 only certain way of showing whether a male whale is immature or mature. Samples of testis tissue, 

 fixed in Bouin's fluid, were sectioned at a thickness of 6 //, and stained with haematoxylin and eosin. 

 The testis samples were not fresh when fixed, for most were collected from whales which had been 

 dead for 18 to 19 hr. and sometimes longer. But there was no difficulty in distinguishing immature 

 tissue, with considerable interstitium and small seminiferous tubules, closed, or sometimes with a 

 small lumen, but always with a simple germinal epithelium consisting only of spermatogonia and 

 Sertoli cells, from mature tissue showing comparatively large tubules, open and with a proliferated 

 epithelium and embedded in a comparatively sparse interstitium. Table 23, p. 271, shows the sub- 

 stantial difference between the diameters of immature and mature testis tubules. Remarks on the 

 male sexual cycle deal with tubule diameters in greater detail (p. 271), but it is relevant here to note 



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