i897. ARE THE ARTHROPODA A NATURAL GROUP? 267 



have cited as holding the Arthropoda together, others which have 

 universal validity and importance, if we except the Peripatoidea. 

 These characters are not in any way difficult to suppose as later 

 developments of conditions already realised in the lower grade repre- 



Class CtiLSS f/tZ5S f/t/ss C'ru-.^ 



HEXAPODA.CHILOPOnA. DlPLOl'ODA. Crustacia. Arachnida 



(Trilobita) 



Grcu^s. CARIDOPHTHALMIA 



c^s. Peripatoiuka 



ora^j. NEREIDOFHTHALMIA 



Sub-f^um. CH/ETOPOD/J 



sub-m/mi. ^RTHROPOM 



/>>4^^ APPENDICULATA 



sented by Pevipattis. Such are the plating and jointing of the body 

 and limbs with dense chitin. Pevipatiis has a soft extensile body, but 

 dense chitin is already deposited on its jaws and claws. It, however, 

 does not actually possess " arthropodous " limbs. Striated muscle 

 and absence of ciliated epithelium go with the increased deposit of 



u 2 



