ACARINA PAEASITES. 451 



animals in his Monographic?, Anoplurorum than any previous 

 observer. He says, "that the opinion entertained of 

 each animal having its peculiar parasite, is not entirely 

 borne out by facts ; nevertheless, that those infesting the 

 quadruped will not be found in the bird, being almost 

 always confined to animals of the same species, or of 

 similar habits. For instance, the DocopJwrus icteroides is 

 found on nearly every species of duck. The Neimus 

 obscurus infests several species of sandpipers, god wits, &c. ; 

 the Neimus rufus, hawks and falcons ; the Docophorus Zari, 

 the gull tribe. In quadrupeds it is rather more doubtful, 

 as they are frequently transferred by association; as an 

 instance, the Trichodectes scalaris has been found upon 

 both the ox and the ass feeding in the same stall. The 

 Hcematopinus piliferus, infesting dogs, have been found in 

 swarms upon the ferret. The PediculuSj besides being 

 found on man, is also found on the Quadrumana, fiodentia, 

 Carnivora, Pachydermata, and the Ruminantia" The 

 family of Ticks (Rwinice) belong to this class, one of which 

 is a great pest to sheep. It is usual to include in this 

 group both Acarina and Parasites ; but from the former 

 having eight legs, and the latter six, with a difference in 

 habits, they are said not to belong to the same family. 



Kespiration goes on simply through the skin in the 

 Acarus and Sarcoptes ; while in Gamasus, Cheyletus, and 

 some others with pincer-shaped mandibles, there is a com- 

 plete system of tracheae with spiracles, as in true insects. 

 Besides these there are others with an intermediate plan 

 of respiration, combining both the before-mentioned 

 modes, and in which inspiration takes place through the 

 skin, and expiration through a system of tracheae, having 

 an outlet above the insertion of the mandibles. Trom- 

 bidium is an example in which a latticed aperture at the 

 root of the mandibles forms the anterior outlet of two 

 large air-pipes running the whole length of the body, 

 each subdivided into a tuft of numerous unbranched 

 simple tracheae ; there is also under the skin a round 

 meshed network of a transparent and seemingly homo- 

 geneous substance, resembling the respiratory network 

 beneath the skin of certain Trematoda. 



The importance of a thorough examination of these 

 GG 2 



