Fhyhgeny of the Arachnida. 301 



with a posterior genital aperture and unsegmented mandibles 

 (Insecta and Chilopoda), while the other was composed of 

 those with an anterior genital aperture and with segmented 

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

 in the former, in many instances unbranched tubular trachete 

 have persisted (Diplopoda, Pauropoda, Symphyla, Arach- 

 noidea). Peripatus 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 possibih'ty 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. 40-i and 

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

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

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

 fact that the whole of tlie Tracheata possess tracheae and 

 Malpighian 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 Liniulus 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 trachetfi 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- 

 da^al 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 

 Perijjatus^ in which in comparison with the Tracheata the 

 anal invagination is very insignificant, has no Malpighian 



* Von Keiiuel seeks to explain each special exception [Peripatus, 

 Japyx, Collembola, Acarina, Pauropoda (?), Tardigrada). 

 Ann. (& Mag. N. Hist. Ser. 6. Vol. xv. 21 



