20 ENTOMOLOGY FOR MEDICAL OFFICERS 



These all make themselves quite at home and behave as 

 parasites ; but they cannot be styled parasites off-hand, since 

 the position is far from being necessary to the existence of 

 the species. They might, perhaps, be called Heniiparasites. 



(iii) A considerable number of predatory Arthropods 

 must be looked upon, so far as man is concerned, as quite 

 casual parasites, since they neither make a point of attacking 

 man nor have any predilection for human dwellings. Such 

 are most mosquitoes, midges, the Siinuliidce, and Tabanidce, 

 and the Reduviid bugs (p. 207). 



(b) Free or Discretionary Parasites. 



Under this head we may collect a considerable number of 

 active predaceous species that habitually live and breed only 

 in human dwellings and outhouses or their vicinity, and 

 either habitually or frequently suck the blood of man. 

 Among such are several species of mosquitoes (e.g. Culex 

 fatigans, Stegomyia fasciata), the maggot of Auchme?-omyia 

 (p. 1 54), several of the blood-sucking Muscidae (e.g. Stomoxys, 

 Hmnatobia), and the bed-bugs. 



It is doubtful whether Glossina and the maggot of 

 Cordylobia (p. 155) should be included here; since, though 

 neither of these shows any adaptive structural differences 

 from its own nearest relatives, yet it is said that Glossina cannot 

 support life on anything but living vertebrate blood, and that 

 the maggot of Cordylobia can live only in the subcutaneous 

 tissue of a living mammal. Both Glossina and Cordylobia, so 

 far as habits go, ought perhaps to be included among the 

 unconditioned parasites. 



(c) Unconditioned or Adapted Parasites. 



Here we must class all those species that not only feed 

 upon human blood and lymph, but also are in some special 

 way modified for clinging to, or sticking to, or burrowing in 

 a host; such as the blood-sucking lice (p. 212), the fleas, the 

 ticks, the itch-mites, the DemodicidcB (p. 268), the Pentastomida, 

 and the maggot ol Dermatobia (p. 182). 



The Hippoboscidce (p. 185) belong to the class of adapted 

 or unconditioned parasites, but they do not, except fortu- 

 itously, attack man. 



