326 THE MICROSCOPE. 



ACAKINA — PAEASITES. 



Nearly all the animals that we include in this order, of which the 

 common Mites are the best known examples, ar^ recognisable at the 

 first glance by the form of the body, which usually c6nstitutes a roundish 

 or oval mass, without any trace of segmentation. They are mostly 

 parasitic animals, furnished with a proboscis containing a pair of sharp 

 spines, which serve for wounding their prey, and bearing a palpus on 

 each side. The proboscis is jointed and -retractile. Sometimes it is 

 furnished with a swollen base, which lias been taken for a head. The 

 eyes, which are often wanting in the parasitic forms, are two in num- 

 ber when present, and are placed on each side of the anterior portion 

 of the body. 



The Acarina are generally oviparous; a few bear living young. 

 The young generally possess only three pairs of feet ; the fourth pair 

 not making their appearance until after the first moult. 



Parasites infest the skin, lurk among the hairs and feathers of 

 quadrupeds and birds, and even of other insect races, whence they 

 draw an abundant supply of support for their singular mode of exist- 

 ence. Mr. Henry Denny has figured and described a greater number of 

 parasitic insects in his Monogra/phia Anoplrn/rorv/m 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 Docophorus.icteroides is to be found on nearly 

 every species of duck. The Wdmus obscurus infests several species of 

 sandpipers, godwits, &c. ; the Ndmus rufus, the hawks and falcons ; 

 ihs- Docophorus lari, all the gulls. In quadrupeds it is rather more 

 doubtful, as they are frequently transferred by association ; for instance, 

 the Trichodeetes scalaris has been found upon both the ox and the ass 

 feeding in the same stall. The HmmMopinus pUiferus, infesting dogs, 

 have been found in swarms upon the ferret. The Pediculiis, besides 

 being found on man, is also found on the Quadrwmcma, Rodentia, 

 Camwora, Pachydermata, and the RwmmcmUa. We include in this 

 group both Acari and Pa/rasUes ; though from the former having eight 

 legs, and the latter six only, they are not generally admitted as belong- 

 ing to the same class of insect life. 



Eespiration goes on simply through the skin in Acarus and Sa/r- 

 coptes ; while in Gamasus, Gheyletus, and various kinds with pincer- 



