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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



separated from the body by a deep con.striction, and in front has the 

 circular mouth-opening or camerostome, through which the mandibles 

 may be extended and retracted. The body is usually oval; the skin soft, 

 occasionally with chitinous 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 arc generally short, five-jointed, and usualh' end in tw^o 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 

 function; 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 mandi- 

 bles are commonly long' and 

 needle-like, fitted for piercing tis- 

 sues; in one genus, however, they 

 have two points, indicating their 

 chelate origin. The female geni- 

 tal aperture is just in front of the 

 anus, which is at tip of the ven- 

 ter. The male aperture is behind 

 the anus, and often near the mid- 

 dle of the dorsum. The penis is 

 very prominent, long, slender, and 

 curved, and is often found par- 

 tially extruded. The internal 

 anatomy of the Cheyletida^ has 

 not l)een thoroughl}^ examined. 

 The digestive tube is simple; the 

 stomach is provided with four 

 large ccjeca. In one genus, &(r- 

 <-oj>fe/'i/s, there is no anus; the food 

 of this mite is of such a nature as 

 to ))e completely digested. The 

 respiratory system is perhaps more complete than that of other fami- 

 lies. There are two large tracheal trunks starting from the beak and 

 extending back to near the tip of the body, each giving ofi' many 

 smaller branches which ramify throughout the body. From some 

 accounts it appears that the main trunks are composed of two or 

 three separate trachef^?. These main trunks are connected to each other 

 near their origins. The spiracles are at the sides of the beak, and in 

 some cases there are two also near the median line. These spiracles 

 are sometimes trumpet-shaped. The nervous system consists of a 

 circle around the oesophagus and ten branches from it, four in front 

 and six behind. Two of these branches go to the beak, others to the 

 legs, and two to the posterior part of bod^^ 



Fig. I.S.— ('HKVi.KTrs wuax. fkum bklmw. 



