157 



Order ARANEIDA (Spiders). 

 ^Order ACABISTA (Mites and Ticks). See pages 158 and 161-162. 



| Order PENTASTOMIDA (Tongue-worms). Parasites. The body worm- 

 like and ringed. Two pairs of retractile hooks at sides of the mouth. 

 Respiration cutaneous. Metamorphosis : the larva unlike the 

 adult. 



Example, "j" Pentastoma taenioides (syn., Linguatula 

 rhinaria). The larvae occur in the liver 

 and the adults in the nasal passages of 

 dogs and other quadrupeds and Man. 

 Europe (Central France). 

 *This Order contains blood-sucking species, 

 i Parasites. 



OIIDER ACARINA (MITES AND TICKS). 



Mention the Special Features of the Acarina. 



The body is generally either oval or round, and com" 

 pressed dorso-ventrally ; it may be covered by a chitinous 

 shield or scutum. The integument is either soft or leathery. 

 The three regions of the body are usually fused together. 

 The front portion of the prosoma may form a distinct 

 * false-head," the capitulum, bearing the mouth-parts 

 (collectively termed the rostrum or beak) which may be 

 concealed within or may project from a depression, the 

 earner ostoma. 



The first two pairs of appendages., the chelicerae or 

 mandibles and the pedipalps, are adapted either for biting 

 or for piercing and sucking. The chelicerae may be chelate, 

 or, as in Ticks, long piercing styles. The pedipalps are 

 generally united together at their bases ; and their inner 

 margins are often hollowed out, so that the two, when 

 applied together, form a sheath enclosing the chelicerae 

 and the hypostome. The adults usually have four pairs 

 of jointed legs which end in one or more claws with suckers 

 At their bases. 



Respiration is by tracheae ; but some aquatic mites 

 breathe through the skin. The sexes are separate. Most 

 lay eggs. The metamorphosis is incomplete ; the larva 

 has three pairs of legs. Many of the Acarina are free-living 



