TJic Anatomy of Opisthopatus cinctipes. 69 



ferences in size cannot be regarded as a sexual character. In this 

 respect these legs differ from the two posterior pairs in PeriiMtopsis, 

 in which genus both are generally smaller in the male than in the 

 female. In Peripatopsis also the legs of the last (genital) pair are 

 always much smaller than the first pair in both sexes. In 0. 

 cinctipes the last pair of legs is used for walking in both the male 

 and female. 



The arrangement of the three large distal papillae on the feet 

 appears to be fairly constant, the dorsal one being placed exactly, 

 or almost exactly, in the middle between the anterior and the pos- 

 terior papilla, but sometimes nearer the former than the latter. The 

 pair of large papillae at the base of the foot is absent, as in the 

 American forms (figs. 14 and lla). 



The proximal spinous pad of the 4th and 5th legs is inter- 

 rupted by the nephridiai papilla, which is quite separated from the 

 two portions of the pad and either lies in a line with them or i& 

 slightly more proximal, as in fig. 12. The nephridiai papilla is at 

 the same time slightly posterior to the middle line of the leg, so that 

 the anterior portion of the proximal spinous pad is larger than the 

 posterior portion, although not so much larger as it appears in the 

 figure, in which the whole of the posterior pad is not visible. 



The nephridia of these legs are much enlarged as usual, and 

 discharge at the apex of the nephridiai papilla. 



4. The jjosterior region of the body. 



In the general appearance of the posterior part of the body 

 Opisthopatus closely resembles the Australasian genus PeripatoideSy 

 especially such forms as P. leuckarti var. orientalis (Fletcher) from 

 New South Wales (c/. figs. 2 and 3). In both these genera not 

 only the postgenital segments, but also the genital segment itself^ 

 are considerably more developed than is usually the case in Peri- 

 patopsis. In the latter genus (figs. 4 and 5) these segments are 

 generally much reduced, this reduction evidently going hand in 

 hand with the abortion of the genital pair of legs. It must be 

 remembered, however, that in a large series of specimens a certain 

 amount of individual variation in the development of the posterior 

 region is observable, which tends to bridge over the differences 

 between the two genera in this respect. So, for instance, in P. 

 balfouri the genital legs are placed much nearer to the hind end 

 of the body than to the penultimate pair of legs in Sedgwick's 

 figure 24 (1888&), while in several of our specimens they are 



