38o DISCOVERY REPORTS 



situated in a deep groove immediately in front of the anus (Plate XXIX, fig. 2, and 

 Plate XXXIII, fig. 3). In immature whales this groove is usually tightly closed, but in 

 mature whales it is generally slightly open so that the clitoris is just visible. On each 

 side of the genital groove are the slits which contain the nipples of the mammary glands. 

 As stated on p. 276, the average distance between the anus and reproductive aperture 

 in, for instance, female Blue whales is 2-6 per cent of the total length, or 0-65 m. in 

 a 25-0 m. whale. The most important observations to be made are probably those 

 concerned with indications of " heat " in females, but we have met with only one case in 

 which a whale appeared to be in this condition. In No. 775 the genital groove was rather 

 more open than usual and the clitoris was pushed outwards by a slight eversion of the 

 vagina. The latter was noticeably congested and contained some clear mucus. The actual 

 presence of mucus appears to mean little, for it is present in most whales and is often 

 found to be issuing in considerable quantities from the vagina, but instead of being 

 clear it is normally cloudy and viscous. 



The condition of the external genitalia may also occasionally be useful in indicating 

 the approach of parturition in pregnant whales. In Nos. 154 and 175 the vulva was 

 greatly swollen and the genital groove stretched open to a remarkable extent as though 

 from considerable internal pressure. These two whales were found to contain foetuses 

 measuring 6-3 and 6-05 m. respectively, and it is to be supposed that parturition was 

 to take place very shortly. 



In the male, the penis is retractile and is normally completely withdrawn into the 

 cavity within the genital groove. The exterior then presents a long groove which differs 

 from that of the female in its shape and in its more forward position (Plate XXX, fig. 2). 

 Whereas in the female the anus lies immediately at the posterior end of the genital 

 groove, in the male there is a considerable distance between the two. The average 

 distance between the anus and genital aperture in this sex is 6 to 7 per cent of the 

 total length, and this measurement gives in fact the most obvious distinction between 

 the sexes. The shape and proportions of the penis are illustrated in Plate XXXIII, fig. i. 

 In the carcasses of males brought to the whaling station the penis is frequently fully 

 extruded, but this takes place gradually, after the whale has been killed, during the 

 period when it is being towed back to the whaling station. In fully grown Blue and 

 Fin whales the penis measures usually from 2 m. to 2-5 m., but adult specimens (e.g. 

 No. 1229) have been recorded in which the penis measured considerably less than 2 m. 



Observations on the size of the penis may be useful as a means of deciding at a 

 glance whether a whale is sexually mature or not, for this organ undergoes considerable 

 growth at maturity. This method, however, is unreliable in the case of whales which 

 have recently been or are about to become mature. 



