422 ENTOMOLOGICAL SOCIETY 



increase over their fellows, the taste becoming fixed, and a variety 

 or species eventually arising. Supposing such a species to occur 

 among dead leaves, and that the source of its food is refuse from 

 the prey of carnivorous animals, there will also occur among this 

 refuse, waste from the body of the carnivora, such as hair, frag 

 ments of epidermis, etc. If the pressure for food come to mites 

 dependent upon this supply, it is easy to imagine them resorting 

 to the bodies of the sleeping animals, to feed upon the loosened 

 epidermis, instead of collecting it, as formerly, from the ground. 

 This habit, temporary at first, will gradually become fixed, and 

 in time the structure would change toward better fitting the 

 mite for clinging to the skin and making its way among the 

 fur, thus gradually becoming adapted to a permanent life upon 

 the bodies of mammalia, though still feeding upon dead tissues. 

 From this to a habit of penetrating into the living skin is but a 

 step, and thus we have the development of a truly parasitic 

 species. This reasoning is purely hypothetical ; but we have, as 

 a matter of fact, in nature, examples of mites illustrating all the 

 stages which have been indicated, namely, vegetable feeders, 

 mixed feeders, scavengers, commensals, and parasites. 



EFFECTS OF THE PARASITIC LIFE. 



Parasitism in its broadest sense means degradation, and in its 

 zoological sense fully bears out this interpretation ; for the result 

 of parasitic life through all its phases, from voluntary but yet 

 essential dependence to the most abject and necessary dependence 

 on the host, involves increasing degeneration. This first takes 

 place in impotence of particular organs, followed by their gradual 

 reduction until, in older parasitic forms, the locomotive organs 

 have entirely disappeared and the mouth-parts are correspond 

 ingly reduced and modified. Yet, consectaneous with this reduc 

 tion or degeneration of locomotive members, we find equally 

 marked specializations of other structures, in the direction of 

 suckers, hooks, and other features which facilitate attachment or 

 adhesion to the host the limbs, mouth-parts, and the dermal 

 covering all taking part in the specialization. 



The morphological characters belonging to the parasitic forms 

 are, moreover, essentially degradational, and the tendency among 



