OF WASHINGTON. 417 



americanus has been found affecting chickens in Texas and the 

 Southwest. 



The Linguatulida are found in the air-passages of vertebrates 

 and the nasal cavities of some domestic animals, especially dogs. 

 Pentastomum has a remarkable life-development and is found in 

 the liver and air-passages of various animals, especially the rabbit 

 and the dog. Cytoleichus affects the air-passages of chickens; 

 Dermatoryctes mutans affects the skin with a sort of itch, while 

 both Syringophilus and Analges live in the quills of their feathers. 

 Dermanyssus is a partial parasite of birds and is known to be a 

 serious pest of canaries. The itch and mange mites (family 

 Sarcoptidae) are known to all, as are also Uropoda and Gamasus, 

 so common on various insects. 



Among the so-called Harvest Mites (Trombidiidae) the adults 

 are but partially parasitic, while the larvaa of many forms, which 

 are six-legged, were previously considered as adults, forming the 

 spurious family Leptidas, and are well known in warm climates 

 as annoyances to man under the popular names Red Bugs and 

 Jiggers. The pseudo-parasitism in this case, however, is not an 

 essential part of the economy of the species, and is in fact a posi 

 tive detriment, since individuals attaching themselves in this way 

 to warm-blooded animals are usually, if not invariably, destroyed, 

 but, when attaching to insects proper, they complete their trans 

 formations. Whether such parasitism on hexapods is absolutely 

 necessary to full development has not been proved, though it is 

 more than probable that such is the case, just as attachment to 

 warm-blooded animals seems essential to the propagation of the 

 ticks. Hydrachna affects water insects in the same way that 

 Trombidium does terrestrial species. 



THE DERIVATIVE ORIGIN OF INSECT PARASITISM. 



That the parasitic insects have been developed from non-para 

 sitic forms is a conclusion which the study of them and their allies 

 fully justifies, and there is no logical method of accounting for 

 them except upon this basis It may be safely asserted that par 

 asitic insects, as such, could not have existed before the animals 

 upon which they live, and this in itself is the best indirect proof 

 of the proposition. It may not be amiss, however, to set forth 



