SECTION XVI 



PERIPATUS AND THE TRACHEATA 



BEFORE closing this essay, in which we have 

 endeavoured to prove that Apus is an almost ideal 

 transition form between the carnivorous Annelids 

 and one large division of the Arthropoda, viz. the 

 Crustacea, it is but fit that we should briefly refer to 

 Peripatus, which is acknowledged to be a transition 

 form between the Annelids and the other division of 

 the Arthropoda, viz. the Tracheata, in which we 

 include the Myriapoda, Hexapoda, and Arachnida. 

 It cannot but add to the interest of this book if we 

 dwell upon this point for a short time. 



The accepted fact that both divisions of the Arthro- 

 poda are derived from Chaetopods, the chief cause of the 

 transformation being the same in both, viz. : the use of 

 the parapodia as appendages for mastication and loco- 

 motion, accounts for the resemblances in the organ- 

 isations of the Crustacea and Tracheata which have 

 led to their being placed side by side as Arthropods. 

 There are, however, striking differences in their 



