ANIMAL PARASITES 171 



of adventitious troubles, conspicuous amonost 

 which is the irritating " tide," which it tries so 

 dihgently to remove by rubbing itself against a 

 gate-post or tree. The sheep-ticlxs, magnified 

 representations ot which are shown in Figs. 1 10 

 and rii, belong to a family of extremely trouble- 

 some creatures which in distribution may be said 

 to be cosmopolitan ; and in tropical countries they 

 reach much greater dimensions than our British 

 species exhibit. Ticks puncture the skin of the 

 animals or birds on which they teed by means of 

 a projecting beak, which is armed with recurved 

 teeth and works in a kind ot sheath, to prevent 

 the escape of blood other than that which the 

 creature is absorbing. The female tick thus 

 pumps herself so full of her victim's blood that 

 she assumes extraordinary dimensions. 



A portion of the life ot the sheep-tick, however, 

 is not spent on the sheep, for they often occur 

 on the ground, and probably to some extent are 

 vegetable feeders. Pairing and hatching of eggs 

 take place usually on the ground beneath stones, 

 and in similar situations. But, when the craviny 

 for blood returns, they climb the stalks of grasses 

 and other plants, and while holding on with their 

 fore-limbs, extend their other legs and hooked 

 claws, which are shown in the illustration, and 

 await the passing ot some woolly sheep, or if the 



