Pliyhgeny of the Arnchnida. 301 



with a posterior p^cnital aperture and unscgmentcd mandibles 

 (Insccta and Cliilopoda), while the other was composed of 

 those with an anterior genital aperture and with segmented 

 mandibles, and in whicli, moreover, contrary to what we find 

 in the former, in many instances unbranched tubular traehcaj 

 have persisted (Diplopoda, Pauropoda, Symphyla, Arach- 

 noidea). Peri'patus forms, in the opinion of this author, a 

 divergent branch from the primitive types (" Peripatiformes "). 

 After von Kennel has thus demonstrated the necessity of 

 dividing the Arthropods into Branchiata and Tracheata, and 

 the possibility of similar characters appearing independently 

 in the organization of Annelids and Crustaceans, he is un- 

 willing to investigate the relation of the Arachnida to the 

 Crustacea (the Merostomata included, cf. No. 26, pp. 40i and 

 405), since he is able to prove the common origin of the 

 whole of the Tracheata (No. 24, p, 18). If we enquire how 

 the latter can be done, we are told that it is proved by the 

 fact that the whole of the Tracheata possess trachese and 

 j\Jalpighian tubes*, and that consequently these organs must 

 have been present in the ancestral form also. It is evident 

 that this method of proof contains nothing new or original, 

 and since every naturalist who sought to prove the relation- 

 ship between Arachnids and Limulus had to deal with cha- 

 racters of that kind, there is in my opinion nothing whatever 

 to justify von Kennel in ignoring similar features in the 

 organization of the Arachnids and the ^Merostomata. If this 

 author had been prepared to handle these conditions, he must 

 of necessity often have had recourse to improbabilities in order 

 to explain the various similar characters ; and this he actually 

 does, so soon as he considers the independent appearance of 

 similar features in the Crustacea, which have been developed 

 directly from unsegmented animals, and in the Tracheata, the 

 descendants of the Annelids. I have already touched upon 

 the question of the development of the tracheoe in the 

 Arachnids, and shall return to it again further on ; now, 

 however, we are dealing only with the Malpighian tubes, 

 which are regarded by von Kennel {loc. cit. p. 23) as 

 nephridia that have been carried inwards with the procto- 

 daial invagination. This view, which owes its origin to a 

 certain functional resemblance between the two structures, is 

 founded by von Kennel only upon the circumstance that 

 Pen'patuSj in which in comparison with the Tracheata the 

 anal invagination is very insignificant, has no Malpighian 



* Von Kennel seeks to explain each special exception {Peripatus, 

 Japyx, Collembola, Acarina, Pauropoda (!''), Tardigrada). 



Ann. cC- Mag. N. Hist. 8er. G. Vol. xv. 21 



