STKUCTURli] AND ULASSJFICATION OP THtl ARTlIKOrODA. 529 



coelomj coelomoducts, and nepliridia^ see the introductory 

 chapter of part ii of Laukester's ' Treatise on Zoology •"). 



Tabular Statement of the Grades, Classes, and 

 Sub-classes of the Arthropoda. — It will be convenient 

 now to give in the clearest form a statement of the larger 

 subdivisions of the Arthropoda which it seems necessary to 

 recognise at the present day. The justification of the 

 arrangement adopted will form the substance of the rest 

 of the present article. The orders included in the various 

 classes are not discussed here, but are treated of under 

 the following titles: — Peripatus (Onychophora), Myeiapoda 

 (Diplopoda and Chilopoda), Arachnida, Insecta (Hexapoda), 

 and Crustacea. 



Sub-phylum ARTHEOPODA (of the IMiylum Appen- 



diculata). 



Grade A. Hyparthropoda (hypothetical forms connecting an- 

 cestors of Chastopoda with those of Arthropoda). 



Grade B. Protarthropoda. 



Class Onychophora. 

 Ex. — P e r i p a t u s. 



Grade C. Euarthropoda. 



Class 1. Diplopoda. 

 Ex. — Jul us. 



Class 2. Arachnida. 



Grade a. Auomomeristica. 



Ex. — Phacops. 



Grade h. Nomomeristica. 



{a) Pantopoda. 



Ex. — Py cnogonum. 

 (&) Euarachnida. 



Ex. — Limulns, Scorpio, Mygale, Aca- 

 rus. 



