BOOK THIRTEENTH. 



AEACHNOIDAE. 



CLASSIFICATION. 



§ 295. 



The Arachnoidae, which are organized after very different types, have 

 always four pairs of feet. The Tardigrada form no exception in this 

 respect ; and although it may appear singular to find them placed in this 

 class, yet this seems their most proper place ; only they should be placed' at 

 the head, for they form the transition of the Arachnoidae to the Annelides, 

 exactly as do the Cirripedia from the Crustacea to the Acephala.* 



The Arachnoidae are usually defined as Arthropoda wanting the anten- 

 nae ; this, however, is incorrect, for these organs are not wanting, strictly 

 speaking, but take the place of the mandibles, which are absent, as will be 

 shown hereafter. 



ORDER I. 



Cephalothorax multi-articulate. Special respiratory organs wanting. 



SUB-ORDER I. TARDIGRADA. 



Legs rudimentary. Abdomen wanting. 



Genera : Milnesium, Macrobiotus, Emydium. 



SUB-ORDER II. PYCNOGONIDAE. 

 Legs very much developed. Abdomen rudimentary. 



Genera : Nymphon, Ammothea, Pallene, Phoxichilidium, Pariboea, Endeis, 



Phozickilus, Pycnogonum. 



* [ § 295.] For a detail of the data wliich fully Stellung der Tardigraden, in Siebold and Kslliker's 

 justify this position of the Tardigrada, see Kauf- Zeitsch. HI. 1851, p. 220. — Ed. 

 mann., Ueber die Entwickelung uud systematische 





