211 



If its feet consisted of yielding substances it would have 

 great difficulty in progression. They are, therefore, furnished 

 with a horny .claw incapable of being injured by a slight acci- 

 dent, and strong enough to be a lever on which the leg can 

 act. As it may be required occasionally to grasp a hair, there 

 is a provision made for this in a small dilatation at the ex- 

 tremity of the tarsus on which the hook may press. I may 

 mention here that the motions of these hooks is confined to a 

 simple approximation to the under surface of the leg, and the 

 reverse — they do not give any lateral power. This is no more 

 than from their attachments might be expected. 



There is another form of louse (Pediculus pubis), whose 

 habitat is not on the surface amongst the hair but on the 

 hair itself. It fixes itself to it very tenaciously by means of 

 its feet, and is with difficulty detached. Its ova are found 

 agglutinated to its habitation, and its sole locomotion is from 

 hair to hair. 



We shall not be surprised to find in it a modification of the 

 simple claw to suit the altered circumstances. In it the foot 

 consists of a vastly enlarged claw, furnished with strong ser- 

 rations, and possessing a large and horny surface on which 

 the claw can be pressed down without injury. By this appa- 

 ratus each hair can be firmly and completely grasped — with- 

 out it the foot would be crushed or otherwise injured. Fig. 4. 



The ephemera has a foot consisting of a single claw, but 

 armed with two rows of spines. Pig. 12. The intention of 

 these is probably to give it greater power in seeking and re- 

 taining prey, or moving along fibrous substances in the water 

 when its gravity would avail it nothing. 



The foot of the Gyrinus natatory or whirligig, consists of a 

 pair of claws, and a rudimentary boss which is perfectly free 

 from hairs of any kind. 



The last joints of the tarsus are developed in such a manner 

 that they may almost be said to be webbed like the foot of the 

 swimming birds. A number of hairs exist also, which assist it 

 greatly when paddling through the water. 



