292 ARTHROPODS. 



The spermatozoa are transferred to the last joint of the 

 male's pedipalps, which are thrust into the receptacle or into 

 the vagina of the female. 



The segmentation of the ovum is centrolecithal, i.e., peri- 

 pheral. A cocoon is usually formed around the eggs, this is 

 often carefully hidden or carried about by the female. 

 There is great maternal solicitude, though there is little 

 conjugal affection. 



Fossil forms are often found imprisoned in amber. 



Examples — 



1. Tetrapneumones, e.g.,Mygale,z.\2x%t lurking spider 



which has been known to kill small birds, but 

 usually eats insects. Atypus, Cteniza, etc., 

 make neat trap-door nests. 



2. Dipneumones, including 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. 

 Argyroneta aquatica fills a sub-aquatic silken 

 nest with air-bubbles caught at the surface. 



Order 7. ACARINA. Mites and Ticks, e.g., Q,\ve,es,e-TmX.e(Tyroglypkm). 



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 cei^halothorax, both are unsegmented. 

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

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

 (il is a puzzle how some of the parasitic mites manage to breathe at all) ; 

 in the majority there are tracheae with two stigmata. 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 tracheEe. Cheese-mite {Tyroglyphus). Itch-mite 

 {Sarcoptes scabiei), causing a loathsome disease. S. cams 

 causes " mange " in dogs. Follicle-mite (Demodexfolli- 

 culorum), common in the hair-follicles and sebaceous- 

 glands of man. Gall-mites {Phytoptus), on plants. 



