CHAKACTERS OF SOME HYSTRICOMORPH RODENTS. 413 



li' . Prepuce not withdrawn into common integumental sac 

 with anus, but remote from that orilice. 

 j. A small pointed soft hippet in the middle line below the 

 urino-s'enital orifice and projecting between its labia, 



as in Ociodon and Ctenomj/s Caprami/s. 



j'. No lappet below the urino-geiiital orifice. 



k. Walls of glandular pouch spicular, not distinctly 

 laminated, with merely two low rounded ridges 



running down the anterior wall Dolicliotis. 



k'. Walls of glandular pouch with numerous compressed 

 ridge-like laminse. 



I. Apex of glaiis broad and truncated CkincJiilla. 



I'. Apex of glans attenuated Myocastor. 



The Genital Organs of the Female. 



The genital apparatus in the female Hijstrioa and Acanthion 

 appeai-s externally as a large triangular prominence, marked on 

 its posterior surface by a longitudinal slit. Separation of the labia 

 of the slit reveals the orifice of the vulva above, and just beneath 

 the latter the orifice of the urethral canal. Some distance beneath 

 the urethra and near the apex of the integumental prominence is 

 a trilobed clitoris, with a shallow glandular depression above or 

 in front of its apex. The lateral lobes can be folded over so as 

 to meet each other in the middle line and form a partial tube for 

 the passage of the urine. In the impaired female only one orifice 

 is superficially detectable above the clitoris. The condition is 

 very similar in J. i^er^M•«, except that the clitoris has a simple 

 conical apex with the orifice of the urethra near its tip, and 

 therefore farther from the vulva than in Hystrix. (Text-fig. 26, 

 A, D, E.) 



In Erethizon and Coendu the anal and genital area of the 

 female is bordered on each side by a ridge of integument running 

 from the root of the tail to the clitoris. The vulva is a tolerably 

 large orifice situated a little below the anus, and the urethra 

 is a smaller orifice beneath the vulva and above the tip of the 

 clitoris, which has a glandular pouch just below and in front 

 of it, and the clitoris is protected by a short projection of hairy 

 integument corresponding to the prepuce of the male. The 

 condition is thus very much the same as that of Hystrix and 

 Atherura. In Coendu the integument round the urino-genital 

 orifices is naked, whereas in Erethizon there is a considerable 

 quantity of hair round the orifices. (Text-fig. 26, F, G.) 



In Myocastor the vulva is an arched transverse orifice close 

 beneath the anus in the middle of the naked area above described. 

 A little way beneath it is the short, conical, slightly hairy clitoris, 

 which is perforated at the tip by the orifice of the urethra, 

 (Text-fig. 27, A, B.) 



In Capromys the vulva is a little way beneath the anus, and 

 below it the prepuce of the clitoris, which is long in the adult, 

 projects downwards and backwards. It has a few hairs at the 

 tip, which bears a large bilabiate orifice. (Text-fig. 27, C, D.) 



In Octodon the vulva is a large transverse orifice close beneath 

 Proc. Zool. Soc— 1922, No. XXYIII. 28 



