336 ARACHNOIDEA AND PAL^OSTRACA. 



Classification of Spiders. 



1. Tetrapneumones. 



Four lung books and no tracheae. 



My gale, a large lurking spider which has been known to kill 

 small birds, but usually eats insects. Atypus, Cteniza, and 

 others make neat trap door nests. 



2. Dipneumones. 



Two lung books and tracheae as well. 



Here are included the web spinners, e.g., Epeira, wolf spiders, 

 e.g., Lycosa, Tarantula, the latter with poisonous qualities 

 which have been much exaggerated ; jumping spiders, the 

 family Attidse, e.g., Attus salticus. The common house 

 spider is Tegenaria domestica ; the commonest garden 

 spider is Epeira diademata. Argyroneta aquatica fills an 

 aquatic silken nest with bubbles caught at the surface. 



Order 7. ACARINA. Mites and Ticks, e.g., Cheese mite ( Tyroglyphus). 



Mites are minute Arachnoids inclined to parasitism. They occur in 

 the earth or in water, salt and fresh, or on animals and plants. They 

 feed on the organisms they infest or upon organic debris. 



The abdomen is fused with the cephalothorax, both are unsegmented. 

 According to the mode of life, the mouth parts are adapted for biting or 

 for piercing and sucking. Respiration may be simply through the skin ; 

 in the majority there are tracheae with two stigmata. A heart seems 

 usually absent, but it is present in Gamasus. Many of the young have 

 only three pairs of legs when hatched, but soon gain another pair. 

 When some mites are starved or desiccated, and to some extent die, 

 certain cells in the body unite within a cyst, and are able in favourable 

 conditions to regrow the animal. 



Examples 



(a) Without tracheae. Cheese mite (Tyroglyphus']. Itch mite 



(Sar copies scabiei], causing a loathsome disease. S. canis 

 causes "mange" in dogs. Follicle mite (Demodex folli- 

 cu forum), common in the hair follicles of man and 

 domestic animals. Gall mites (Phytoptus], on plants. 



(b) With tracheae. Harvest mites (Trombidium), minute para- 



sites often troublesome in summer. What is often called 

 the red spider ( Tetrarhyncus telearius], spins webs, and 

 lives socially under leaves. Water mites, e.g., Hydrachna, 

 on water beetles, and Atax, on gills of fresh water mussels. 

 Beetle mites (Gamasus), often found on carrion beetles. 

 Ticks (Ixodes], on dogs, cattle, &c. 



Aberrant Orders or Classes. 

 Order 8. LINGUATULIDA. Pentastomum tanioides. 



This strange animal is parasitic in the nasal and frontal cavities of 

 the dog and wolf. It is worm-like in form, externally ringed, without 

 any oral appendages, but with two pairs of movable hooks near the 



