AFFINITIES. 153 



aatennse. Specimens were subsequently obtained from other 

 parts of the Neotropical region and from South Africa^ and 

 the animal was variously assigned by the zoologists of the day 

 to the Annelida and Myriapoda (vide Moseley, No 22, and 

 Sclater, No. 41). Its true place in the system, as a primitive 

 member of the group Arthropoda, was first established in 1874 

 by Moseley (No. 18), who discovered the tracheae. It was 

 reported from Australia in 1869 by Saenger (No. 15), and 

 from New Zealand by Hutton (No. 19) in 1876. The 

 nephridia were first discovered by Saenger (No. 15), but they 

 were re-discovered and more fully described by Balfour (Nos. 

 21 and 28). Gaffron was the first to observe the cardiac ostia 

 and the cilia in the generative tracts. The development has 

 been worked at by Moseley (No. 18), Hutton (No. 19), 

 Balfour (No. 28), and more in detail by Kennel (Nos. 32 and 

 33), Sheldon (No. 45), Sclater (No. 46), and myself (No. 39). 



There can be no doubt that Peripatus is an Arthropod, for 

 it possesses the following features, all characteristic of that 

 group, and all of first-class morphological importance. (1) The 

 presence of appendages modified as jaws. (2) The presence of 

 paired lateral ostia perforating the wall of the heart and putting 

 its cavity in communication with the pericardium. The import- 

 ance of this feature as an Arthropod character was first pointed 

 out by Lankester. (3) The presence of a vascular body cavity and 

 pericardium (hsemocoelic body cavity). (4) The inconspicuous 

 character of the coelom in the adult. Finally, the tracheae, 

 though not characteristic of all the classes of the Arthropoda, 

 are found nowhere outside that group, and constitute a very 

 important additional reason for uniting Peripatus with it. 



Peripatus, though indubitably an Arthropod, differs in such 

 important respects from all the old-established Arthropod 

 classes, that a special class, equivalent in rank to the others, 

 and called Prototracheata, has had to be created for its sole 

 occupancy. This unlikeuess to other Arthropoda is mainly 

 due to the Annelidan affinities which it presents, but in part 

 to the presence of the following peculiar features : (1) the num- 

 ber and diffusion of the tracheal apertures, (2) the restriction 



