MALE GENITAL SYSTEM: EXTERNAL 3 6 7 



fold of skin at the base of the terminal cone a "praeputium" and to reserve the term 

 " penis sac " for the genital slit. The reasons for this will be stated when the homologies 

 of the terminal cone are discussed. 



The "penis sac", into which the penis is normally withdrawn in the adult, does not 

 make its appearance until fairly late in foetal life. In foetuses less than about 3 m. in 

 length the penis projects free upon the surface of the abdomen. In the smaller of the 

 two foetuses examined in the present work (1-23 m.) the penis was quite free and no sign 

 of the penis sac was to be seen. In the larger foetus (2-65 m.) the sac was foreshadowed 

 by a distinct triangular insinking of the body wall in front of the penis, forming a sort 

 of socket into which the organ fitted. It may thus be assumed that the penis sac is a 

 secondary feature of the genital system of the Cetacea. In the stallion the penis is 

 retractile into a similar fold of skin by means of a pair of retractor muscles, as in the 

 Cetacea. In some Marsupials, some Insectivora, Felidae, Elephas and Tylopoda (Weber, 

 1904, p. 260) the penis lies in a sac, which, however, also includes the anus and is 

 surrounded by a sphincter cloacae. The penis in these animals emerges backwards and 

 becomes turned forwards during erection, so that no comparison can be drawn between 

 them and the Cetacea. 



At a point situated about two-thirds of the distance from the base of the penis to the 

 anus, opposite the caudal extremities of the posterior genital grooves, is a pair of small 

 lateral pits. In the foetus 1-23 m. in length they were i-o cm. apart. 



These are the rudimentary male nipples. In the foetus 2-65 m. long they had nearly 

 disappeared and were seen only as a pair of very shallow depressions 9-0 cm. apart. 

 In the adult they are absent. Sections failed to reveal any trace of glandular structure 

 in the pits except for a slight vascularity of their walls. 



The male mammary apparatus appears less developed in Balaenoptera physalns than 

 in B. rostrata, where, according to Kiikenthal (1893, p. 356), the male nipple develops 

 as far as the formation of a mammary sac, such as is found in the female foetus during 

 the development of the nipple. Later the sac is reabsorbed in the male. In the Porpoise, 

 however (Kiikenthal, 1893, p. 356), the male nipple rudiment still exists in the adult 

 and its development proceeds yet a step further. A papilla forms at the base of the sac. 

 In Platanista gangetica a sphincter develops around the opening of the sac. 



The following are the measurements of the external genitalia of the two male Fin 

 whale foetuses dissected. 



Length of body (tip of snout to notch of flukes) ... 2-65 m. 1-23 m. 



Length of penis (base to tip) 14-7 cm. 



475 cm. 

 (partly retracted) 



Diameter of penis at base 3-0 cm 



Diameter of penis at praeputium 1-2 cm. 



Distance from the base of the penis to anus ... 15-3 cm. 8-o cm 

 Distance from the base of the penis to the mid- 

 point between the nipples 101 cm. 



Distance between the nipples o-o cm. 



3-0 cm. 

 i-o cm. 



