210 



It will be seen at once by a reference to the diagrams that 

 the feet of insects may be divided into two distinct classes. 



Those with claws only, and those with claws and an addi- 

 tional adhesive apparatus. 



The first division consists of many varieties, commencing at 

 the simple hair passing through the simple hook, the double 

 hook, the double and serrated hook, to the more complex 

 foot of the second order. 



Beginning with the most simple forms, we find that the 

 foot of the Acarus scahiei, fig. 18, or itch insect, consists of 

 two simple hairs — one short and one long. Its habitat is in 

 the foUicles of the skin, where there is no necessity for pro- 

 gression j a complicated foot would be of no advantage, and 

 hooks would })robably prevent its moving readily in its con- 

 tracted domicile. 



The harvest bug — an animal whose habitat is beneath the 

 human skin, through which it has an instinctive propensity 

 to burrow — is equally without claws, but the hairs which 

 supply their place may be said to form a connecting link be- 

 tween hairs and claws. They are fine and small, but decidedly 

 curved in shape. Pig. 1. 



A further connecting link may be seen in the Entomostraca. 

 These possess many pairs of feet. Each pair seems to have a 

 definite object : the first and second pair are used for convey- 

 ing food to the mouth, others for swimming, and others for 

 progression when they are creeping. Figs. 38, 34, 35, 36, 37. 



The hairs with which each pair are furnished differ mate- 

 rially from each other, but are in no case specially strength- 

 ened so as to become claws. 



Few things can be better adapted for swimming than the 

 feathery hairs of the swimming legs. 



We find the simple claw appearing in the ordinary louse. 

 Fig. 3. This creature, it is well known, infests the surface 

 of the skin, and crawls about amongst the hairs with which 

 the body is every where more or less covered. 



