240 DISCOVERY REPORTS 



The cestode Tetrabothrius affinis is nearly as commonly found, and is usually present 

 together with Balaenoptera iurbwella. Its presence was noted in 158 out of 192 whales 

 examined, and the infection was heavy in 33 per cent. It was found only in the intestine. 

 B. hirbinella and Tetrabothrius affinis occur with equal frequency in Sei whales at South 

 Georgia and at South Africa. 



In the seasons 1928-9 and 1930-1 at South Georgia a closer examination was made 

 for internal parasites, and in the 1 15 Sei whales examined in these seasons the following 

 additional parasites were found : 



Tetrabothrius fwilsoni {=Oriana wilsoni) in the intestine on three occasions. 



A large dibothriid cestode, apparently unnamed, occurred sometimes in quantity in 

 the intestine in twenty cases. This parasite is very much commoner in Fin and Blue 

 whales. 



On two occasions Priapocephala grandis was found in the intestine. 



The trematode Ogmogaster plicatus was found in the rectum of five whales. 



Seventeen whales had nematode worms in the kidney and ten males had nematodes 

 in the erectile tissue of the penis and in the urethra. 



Lastly, nematode worms were found encysted in the wall of the stomach in one whale. 



REPRODUCTION 

 THE MALE 



External genitalia. The penis of the Sei whale, cylindrical and tapering to a point, 

 is lodged in a median groove situated at a distance of about 7-0 per cent of the body 

 length in front of the anus. It is normally retracted within the groove, but after death it 

 frequently becomes extruded when the whale is drawn up out of the water on to the 

 flensing plan. It is large in proportion to the size of the animal, being as large as that 

 of the Fin whale and measuring up to i-86 m. in length. It is usually pigmented only 

 at the base, or else entirely unpigmented. 



Testes. The approximate volume of the testes, in thousands of c.c, obtained by 

 multiplying together the length, breadth and depth, is plotted against the total length 

 of the whale in Fig. 68. The curve is that for the mean values of volume for every half 

 metre increase of total length. The volume of the testis increases slowly before maturity 

 is reached between 13 and 14 m. of total length, after which the volume increases 

 greatly. The mean volume of the testis is nearly proportional to the size of the whale, 

 but individual variation is very great. No correlation can be traced between this wide 

 variation and either the age or condition of the whale, or the season of the year. Testes 

 of small size frequently appear to be in quite as high a state of activity as the largest. 

 The largest testis volume recorded for this species, 20,280 c.c, is rather more than a 

 third of that found in Fin and Blue whales. 



Sexual cycle. Histological material from the genitalia is available from twenty-four 

 adult male Sei whales, and the results of its examination are shown in Table XVIII. 

 The minute structure of the testis is essentially similar to that of the Fin and Blue 

 whales and consequently need not be particularized here. 



