TWO NEW SPECIES OF ONTCHOPHORA. 525 



It lias been mentioned above as a general principle that 

 animals which are primitive in some respects need not of 

 necessity be so in all respects. The primitive genus Eo- 

 peripatus has the most primitive kind of ovum, while the 

 almost equally primitive genus Peri pat us has completely 

 lost its food-volk, and in consequence the embryo has assumed 

 an entirely secondary mode of obtaining nutriment. This 

 seems to be equally true of Paraperipatus, where one portion 

 of the ovum is turned into a kind of trophic sac, which comes 

 in contact with the uterine wall and draws nutritive material 

 from it, by means of which the young embryo develops and 

 increases in size. 



We now pass on to discuss the relations of the various 

 genera to one another. 



VI. The Relations op the Various Genera op the Peripa- 



TID.E TO ONE ANOTHER, TOGETHER WITH SOME PhYLOGENETIC 



considerations. 



M. Bouvier, in his recently published memoir, has put 

 forward the view that the most primitive forms are those 

 which show the least amount of degeneration of the two 

 pairs of legs situated posteriorly (5). He is of opinion that 

 there is a gradual degeneration of the last and penultimate 

 pairs of legs, and fi-om this point of view the family Peri- 

 patidie naturally falls into four sub-families (see pp. 480 to 

 484). This view is accepted without reserve in the present me- 

 moir. It seems so well founded that there is no need to say 

 anything in its favour. However, it may not be out of place to 

 point out one embryological fact which supports this view, 

 namely, the pi-esenoe in P. capensis of two vestigial somites 

 behind the somite of the anal papillaa or last pair of legs (14). 

 This is the exact number that is wanted in tliat species to 

 represent the segments found by Kennel in the Neotropical 

 forms. They completely disappear in the former, but in the 

 latter the hinder somite, that is, the anal somite, gives rise to 

 a vestigial renal organ in the female, and to the anal glands 



