CHARACTERS OF SOME IIYSTRICOMORPH RODENTS. 419 



In Ccelogenys the anus forms a large prominence near the middle 

 of a naked area of skin which extends in front of the tail above 

 and of the penis or clitoris below. The anal glands are repre- 

 sented externally by a pair of small pouches opening one on each 

 side of the termination of the rectum Avithin the sphincter of 

 the anus. (Text-fig. 28. D.) 



Dasyprocta seems to resemble Ccelogenys in having paired 

 lateral anal glands. 



The anus in bp.th sexes of DoUchotis is in the upper half of an 

 area of naked skin which extends inferiorly beneath the genito- 

 urinary orgaiis, and is separated from the tail above by a fringe 

 of hairs. When the anus is opened the orifices of the anal 

 glands appear as a pair of oblique slits set one on each side above 

 the termination of the rectum. The orifice leads into a shallow 

 hair-lined pouch. (Text-figs. 23, A, B ; 28, C.) 



In Cavia porcellus the anus is situated near the summit of a 

 large naked area which extends downwards to the prepuce in 

 both sexes ; but it is normally concealed from view by being- 

 folded into a depression common to it and the anal glands. This 

 depression appears superficially as a median groove. When this 

 is dilated it resolves itself in the female into a pair of pits 

 separated by a low partition, and situated between the anus and 

 the vulva. In the male the pits are much larger and longer 

 and when distended to the fullest extent appear as a single 

 capacious pouch owing to the depression of the partition between 

 them. When partially closed the floor of the pouch rises to 

 form a low partition between the pouches. A female C. aperea 

 resembles 0. po?'ceUus in the features mentioned above. But a 

 male example of Gcdea littoralis difiers very considerably from 

 the male of C. porcellus. The anus is at the summit of a large 

 naked or nearly naked area extending down to the penis ; but 

 this area, overlying the testes, shows no trace of glandular 

 depression, the anus being exposed, as in Dasyprocta and other 

 genera. I failed to find the anal glands in a spirit-preserved 

 specimen. Kerodon apparently resembles Cavia in the structure 

 of the anal region, but I have seen no fresh material, (Text- 

 figs. 23, F-H ; 28, B.) 



In both sexes of Hydrochcei'us the anus and external genitalia 

 are packed closely together, as if contained by a common sphincter, 

 upon a nearly naked prominence, some distance beneath the tail. 

 Between the anus and the penis or vulva there is a short perineal 

 area, hairier in the male than in the female, and on each side of 

 this lies a long vertical slit which leads into a large pouch, lined 

 with hair, which pi-ojects from the orifice, and filled with secre- 

 tion. At the bottom of each of these pouches there is a strip of 

 naked skin with a row of four or five little pits, and beneath 

 this strip the dermis is thickened and glandular. (Text-figs. 24, 

 A, E ; 28, A.) 



In Otenodactylus the anus opens just beneath the root of 

 the short, tapering, unifor-mly hairy tail, at the summit of an 



