26 



REPOKT 108, U. S. DEPARTMENT OF AGRICULTURE. 



Fig. 24.— Cheyletus sp 

 latt.) 



Superfamily TROMBIDIOIDEA. 



Family CHEYLETID^. 



The Cheyletidae are a small family of tiny mites, differing considerably in habita 

 and structure among themselves. The typical forms are distinguished by the enor- 

 mous palpi attached to a distinct beak. The palpi 

 are three to five jointed, and frequently have a 

 minute movable tubercle or papilla near the tip 

 on inner side, which in some forms is tipped "vrith 

 one or two pectinate bristles. This papilla is evi- 

 dently homologous with the "thumb" of the 

 Trombidiidae. The beak is plainly separated from 

 the body by a deep constriction, and in front has 

 the circular mouth opening or camerostome, through 

 which the mandibles may be extended or re- 

 tracted. The body is usually oval; the skin soft, 

 occasionally with cliitinous plates, and in many 

 forms finely striate. The division between the 

 cephalothorax and abdomen is rarely present. The 

 body bears a few hairs, sometimes in the form 

 of scales. The legs are generally short, five- 

 jointed, and usually end in two claws, with a 

 bunch of hairs or a pectinate bristle between 

 them. In some species the front legs terminate 

 in bristles and appear to have a tactile func- 

 tion; in others the front legs are transformed into 

 clasping organs. Sometimes there is an eye on each side of the cephalothorax, but 

 it is not often distinct. The mandibles are commonly long and needlelike, fitted 

 for piercing tissues; in one genus, however, they have two points, indicating their 

 chelate origin. The female genital aperture is just in front of the anus, which is at the 

 tip of the venter. The male aperture is be- 

 hind the anus, and often near the middle of 

 the dorsum. The penis is very prominent, 

 long, slender, and curved, and is often found 

 partially extruded. The internal anatomy of 

 the Cheyletidae has not been thoroughly ex- 

 amined. The digestive tube is simple and the 

 stomach is provided with four large caeca. In 

 one genus, ITarpyn/nchus, there is no anus; the 

 food of tliis mite is of such a nature as to be 

 completely digested. The respiratory system 

 is perhaps more complete than that of other 

 families. There are two large tracheal trunks 

 starting from the beak and extending back to 

 near tlio tip of tlic body, each emitting many 

 smaller branches which ramify throughout the 

 body. I'Voni some accounts it appears that 

 the main trnnks are comj)oHed of two or three 

 Heparatc trajheie. These main trunks are con- 

 nected to eac-h other m^ar their origins. The spiracles are at the sides of the beak, 

 and in some cases there are two others near the median line. These spiracles are 

 sometimes trumpet-shaped. The nervous system consists of a band around the 

 CEsophagUH and 10 branches from it, 4 in front and 6 ])ehind. Two of these branches 

 go to the beak, others to the legs, and two to the posterior part of the body. 



Fig. 2b. — Cheyletus pyriformis: Beak and pal- 

 pus, tip of leg I, and claws of leg II. (Au- 

 thor's illustration.) 



