492 



ARACHNIDA. 



Oribatidce, oviparous. The young are usually hatched with only 

 three pairs of legs, and undergo a metamorphosis, which in 

 the Hydrachnidce is distinguished by several larval and pupal 

 stages (tig. 382 a, 6). Very many Mites are parasitic on animals 

 and plants, others are predacious and live some on land and others 

 in water. 



Fam. Dermatophili. Small elongated mites with long vermiform, trans- 

 versely ringed abdomen, with suctorial proboscis, styliform jaws, and four pairs 

 of short, two-jointed stump-like feet. The only known genus, Demodex 

 (Simonea), lives in the hair follicles of domestic animals (Dog. Cat. Sheep, 

 Cow, Horse), and as D. follicidorum Sim. in the hair follicles of Man, where 

 they may give rise to comedones (fig. 384). 



Fam. Sarcoptidse. Itch mites. Body microscopic in size, stout, and with a soft 

 skin, with chitinous rods for the support of the appendages. 

 There are no eyes. The oral apparatus consists of a suc- 

 torial cone with chelate chelicera? and short laterally-placed 



pedi palpi. The legs are short and 

 stump-shaped, and some or all of 

 them have stalked suctorial discs. 

 The males often have suckers and 

 processes at the posterior end of 

 the body. The females have a 

 special vulva and receptaculum 

 seminis. They live upon or in 

 the skin of Vertebrates, and occa- 

 sion the itch and mange. Sur- 

 coptcs sciibiei Dug. (fig. 385), itch 

 mite. AYitli numerous pointed 

 tubercles, spines and hairs on the 

 dorsal surface. Legs five-jointed., 

 the two anterior terminate with 

 stalked sucker ; the last pair of 

 legs in the male ends not, as in 

 the female, in a bristle, but in a 

 stalked sucker (fig. 385). The 



the vine (after H. Lan- females only bore deep passages 

 dois). Ov, Ovaries; A, j u the epidermis, at the end of 

 anus; Go, genital opening; whi( . h they ^ &nd pmluce by 



their pricking the skin disease 

 known as the itch. The young, 

 when hatched, possess only three pairs of legs and undergo several moults. 

 The domestic animals are infected by different species of Sarcoptidai, which 

 may be temporarily transferred to man. DennatoAectes com munis Fiirst. fy-m- 

 li'mt/'x ctjiti Girl. (fig. 386). 



Fam. Tyroglyphidae. Cheese-mites. Of more elongated form, with conical 

 proboscis, chelate chelicerse, and three-jointed pedipalpi. The five-jointed legs 

 are tolerably long, and have lobes for attachment and claws. Large suckers, 

 especially in the male, are often present at the sides of the anus. They live 

 on animal and vegetable matters. Tyroglyphus xlro Gerv. 



FIG. 383. Female of Phytop- 

 pns rifis, from the leaf of 



'", JB IV , third and fourth 

 pair of legs. 



FIG. 381 Demodex 

 folliculorum (after 

 Mgnin), strongly 

 magnified ; i7, 

 pedipalpus. 



