4o6 DISCOVERY REPORTS 



to examine the matter as closely as possible. It should be explained first that for con- 

 venience the size of the testis may be represented by a number obtained by multiplying 

 together the length, breadth and depth measured in centimetres. This gives a rough 

 approximation to (actually rather more than) the volume of the testis in cubic centi- 

 metres. The size of the smallest testis of a Blue whale recorded in this way was 330 

 (No. 594) and of a Fin whale 300 (No. 705). The largest testes were of a Blue whale 

 58,000 (No. 1331) and of a Fin whale 56,000 (No. 51). As an accurate representation of 

 the size of the testis is unnecessary a figure may be used giving the number of thousands 

 of cubic centimetres in the approximate volume. Thus the largest Blue whale testis 

 may be considered to measure 58, and the smallest 0-3. 



^ — -^ ^ ' 2, 



17 18 19 20 21 



LENGTH OF WHALE IN METRES 



Fig. 139. Size of the testis in Blue whales of different lengths. 



As was to be expected, the size of the testis up to a point varies with the size of 

 the whale, this being in part due to the fact that the former becomes much larger 

 at the advent of sexual maturity. Fig. 139 shows the testes of 180 Blue whales plotted 

 according to the size of the testis and the length of the whale. It will be seen that up 

 to a length of about 23-5 m. there is a general tendency for the size of the testis to 

 increase, but from 23-5 m. onwards it cannot be said that there is any correlation 

 between its size and the length of the whale. The plotted points represent all the Blue 

 whale testis measurements which have been taken (in large numbers of immature 

 whales of course the testes were not examined) and are plotted therefore quite irrespec- 

 tively of the time of year. It is to be supposed from Fig. 139 that during immaturity 

 the testis increases its size ver}' slowly, but that when sexual maturity is reached (around 

 22-5 m.) it rapidly increases in size, and continues to increase over the period during 

 which the whale increases its length by one or more metres. Among whales over 23-5 m. 



