MANUAL OF NATURAL HISTORY. 269 



abdomen not furnished with lateral or anal appen- 

 dages ; mouth with a retractile sucker, or in the form 

 of a fissure with two hooked mandibles. 



I. SUB-ORDER. — Suctorial-Parasites (Suctoria). 



Mouth tubular, rostrate, enclosing an instrument 

 for suction. 



1. Family. — Lice-proper (Pediculidse). Antennae 



filiform, as long as the thorax ; a single eye 

 on each side ; muzzle terminal, short, with a 

 retractile sucker; tarsi of a single joint, ending 

 in a folding hooked claw. 



II. SUB-ORDER.— Jawed-Parasites (Mandibulata). 



Mouth composed of two lips and two hooked 

 mandibles, 



2. Family. — Bird-Lice (Nirmidse). Antennae small, 



shorter than the head ; eyes one or two on 

 each side ; mandibles two, hook-like ; mouth 

 inferior, sometimes a little below apex of 

 head, sometimes sub-central, rimate, with 

 two lips. 



AEACHNIDANS. 



Baron Walckenaer, the greatest authority on 

 this class of animals, justly conceiving the intimate 

 relation that must exist between the organization 

 of these creatures and the webs they spin, has di- 

 vided them into sedentary and wandering Spiders. 



