278 Arthropoda. 



pupates immediately after birtli. On the Horse (and Cow) the active, winged 

 Horse-tick {Hippohosca eqiiina) is found; in the wool of Sheep, the wingless 

 Sheep-tick (Melophagus ovinus). The same mode of propagation is followed 

 by the closely allied, small, blind, wingless Bee-louse {Braula cxca) parasitic 

 on Honey-bees. 



The Fleas {Aphaniptera) are usually placed close to the Diptera, thoiigh 

 probably incowectly. The body of these Insects is compressed, the coloui- bright 



yellow to dark brown, the head small with a 

 1 single ocellus on each side (instead of the com- 



pound eye), the antennae small, clavate, and lying 

 in a pit behind the eye. The mouth-pai-ts ai-e 

 adapted for sucking, but ai-e very different in 

 stnictui-e from those of the Diptera. The actual 

 sucking-tube consists of the very long labnim 

 which is grooved ventrally, and the two mandibles, 

 which form a half -open tube ; the first maxillse 

 ai-e short, pointed, and provided with a foui-- 

 jointed palp of considerable length ; they foi-m, 

 together with the labiimi which can-ies two thi-ee- 

 jointed palps, a kind of sheath for the time 

 sucking-tube ; a hypopharynx is absent. There 

 are three distinct thoracic segments each beai-ing 

 a pair of long powerful legs (the hind legs being 

 Pig. 226. Puletc irritans. somewhat stronger than the others) with very 

 1 imago, 2 larva, 3 pupa. — large cOxse and pentamerous tarsi ; they are 

 After Tasohenberg. apterous. They live as parasites upon Mammalia 



and Birds. The larvse have neither eyes nor 

 legs ; the whitish body is cylindrical, somewhat haiiy ; the mouth-parts are 

 biting ; before pupating they spin cocoons. They live in sweepings, etc. Pulex 

 irritans is a parasite upon Man ; and other species of the same genus also 

 occur upon various other animals. The Chigoe or Jigger {Sarcopsylla 

 penetrans) of the tropical regions of America sucks the blood of Man and 

 other animals ; the fertilised female bores into the skin, and as the ova develops 

 the abdomen enlarges enonnously, reaching the size of a pea ; the apertiu'e 

 into the small cavity in the skin in which the parasite is situated is filled up 

 by the hind end of the body, so that the eggs can be conveniently deposited ; 

 after oviposition it dies. 



Class 4. Arachnida. 



Tlie body is divided into a ceplialothorax and an apodous 

 a b d cm e n . The cephalothorax is usually unsegmented ; the 

 abdomen, which is generally short, is segmented in some forms, 

 unsegmented in others ; sometimes the two regions are separated by a 

 deep constriction (in the true Spiders), but usually there is no distinct 

 separation : sometimes the whole body is fused into a single 

 unsegmented mass (in the Mites).' The cephalothorax is usually 

 furnished, anteriorly, with a varying number of ocelli, grouped in 

 different ways, compound eyes are never present. A n t e n n ee are 

 absent. There are two pairs of jaws, termed the chelicerse and the 



