STRUCTURE AND HABITS 173 



The four pairs of legs are segmated and 

 usually end in claws, but these may be replaced 

 by a sucking-disc. 



The claws are wonderfully adapted for cling- 

 ing round the hairs of animals upon which 

 they may be living as ectoparasites. 



The creatures are classed with the Acarinai 

 and are looked upon as ticks. 



It is thought that originally they were 

 vegetable feeders. Even now they feed on 

 vegetable matter, but are ever ready to attach 

 themselves to animals and to perforate the 

 skin with their saw-edged trunks. Cattle and 

 snakes are their chief victims. 



They are greedy creatures, and will suck 

 blood to such an extent that their bodies 

 sometimes swell to the size of a small walnut. 



They have a large plate on each side of 

 the ventral part of the body, which may act 

 as a sucker of attachment, or it may do similar 

 duty to that of the spiracle of the water 

 beetle, noticed in another chapter. 



This sucker-plate forms a very beautiful 

 object for the microscope. 



