The Anatomy of Opistliopatus cinctipcs. 95 



opening lying behind the last pair of legs has been evolved from 

 forms v^hich had this opening between the legs of the last pair. 



Direct evidence of former postgenital legs is afforded by the 

 presence in the males of most of the genera of accessory glands, 

 representing nephridia (or possibly crural glands) of postgenital 

 segments. The question as to w^hether these glands are derived 

 from nephridia or from crural glands is immaterial, as in either case 

 they w^ould be indicative of the former existence of appendages on 

 the segments in which they occur. 



12. The ancestral form of the Omjchophora. 



If the views set forth in the preceding paragraphs are as correct 

 as I believe them to be, it is evident that the nearest approach 

 amongst living Onychophora to the common ancestral form, as 

 regards the development of the posterior segments of the body, is to 

 be found in the genus Peripatus, as represented by P. eclioardsi, 

 trinidadcnsis, and numerous other, mainly Neotropical, forms (see 

 fig. 1). The condition of these segments in the other genera have, 

 therefore, originated by the successive reduction of posterior legs, 

 glands, and segments, as may be at once seen by comparing the 

 diagrams given in figs. 1-5, bearing in mind, however, that the ances- 

 tral form doubtless also possessed crural glands in the genital segment 

 from which the accessory glarids of that segment in certain living 

 forms have been derived. And I am strongly inclined to believe 

 that in respect to various other parts of their organisation the general 

 tendency in the Onychophora has also been towards simplification 

 and reduction. The organisation of Peripatus is certainly the most 

 complicated of all living Onychophora, and we would, I believe, be 

 justified in considering the form of any particular organ as it appears 

 in this genus to-day, as probably (although, of course, not neces- 

 sarily) more nearly like that of the ancestral form than the same 

 organ in another shape in a different genus would be. With regard 

 to some organs, this appears fairly clear; thus the coxal organs, 

 the elongate spermatophors, and the more complicated form of 

 receptaculum seminis, are probably primitive, and have been lost 

 in those forms which do not now possess them. In the case of 

 certain other organs, however, such as the receptaculum ovorum 

 and the non-follicular ovary, which are peculiar to the genus Peri- 

 patus, it is impossible at present to form an opinion as to whether 

 they represent primitive or newly-acquired characters. 



As is well known, remarkable differences also exist in the structure 



