CHAPTER X 



THE MITES 



Class II. Arachaida. Arthropoda (p. 13). — The arachnids may at 

 once be distinguished from the insects by the relationship of the body 

 parts and the number of ambulatory appendages, as to be described. 



The regions of the body are more or less fused, the head being com- 

 monly fused with the thorax to form the cephalothorax (Fig. 62) , 



The abdomen is in some forms segmented (scorpions), in others un- 

 segmented and separated from the thorax by a deep construction (true 

 spiders). 



Sometimes the cephalothorax and abdomen are fused into one un- 

 segmented body (ticks and mites) . 



In the adult there are four pairs of locomotor appendages, usually 

 seven-jointed, attached to the cephalothorax. There are no wings. 



Antennae are absent. 



The mouth parts are paired chelicerse and pedipalpi, the first in front 

 of the mouth, the second to the side. 



The chelicerse are short, consisting of two or three joints. The last 

 joint may have a claw-like termination for piercing and introducing 

 poison into prey (spiders), or it may be in the form of small chelae (scor- 

 pions). 



The pedipalpi are longer and more like the appendages for locomo- 

 tion. The terminal segment may be strongly chelate (scorpions). 



The eyes are located anteriorly upon the cephalothorax and consist 

 of a varying number of ocelli. The eyes are never compound. 



The skin is of a leathery consistency and is not so hard as in insects. 



Respiration is either by tracheae or by so-called book-lungs, the latter 

 consistmg of a series of invaginations of the skin closely applied like the 

 leaves of a book. Either one or both of these forms of respiratory organ 

 may occur in a single individual. 



Most arachnids are oviparous. In aberrant forms, as Linguatulida and 

 Acarina, certain adult appendages are acquired after a molt. 



The class Arachnida includes the scorpions, spiders, ticks, and mites. 



The two parasitic orders are Acarina, which includes the ticks and 

 mites, and Linguatulida, containing the species Linguatula rhinaria. 



Order I. Acarina. Ticks and Mites. — Arachnida (p. 94). These are 

 small, freciuently microscopic, arachnids iii which there is generally no 

 distinct demarcation l^etween the cephalothorax and abdomen, the body 

 regions being massed into one. 



