A SYNOPSIS OF AUSTRALIAN ACARINA RAINBOW. 151 



.group shall have been systematically worked out. Banks points 

 out that they differ considerably in habits and structure aiiKjng- 

 themselves. 8ome are predacious, and some parasitic ; a few 

 <jccur upon some animals to prey upon the jjarasites of the host. 

 The existence of parthenogenesis has been recorded in respect of 

 several of the Cheyletidse. Banks states that " in one genus 

 SarGopte7'us, there is no anus ; the food of this mite is of such a 

 nature as to be completely digested."** The animals upon whicli 

 Cheyletidje occur are the house and field mouse, several birds, and 

 bats. Some live in cavities or little cells beneath the skin and 

 hair follicles. The eggs, singly or in clusters, are attached to the 

 hairs of the respective hosts, and some species secui'e their ova by 

 spinning a small web over them. 



The CheyletidjB are distinguished by their long beak and 

 enormous palpi ; the latter may be three or five-jointed ; in some 

 species each palpus is furnished with a minute movable tubercle 

 or papilla near the tip on the inner side, and this is occasionally 

 tipped with one or two pectinate bristles ; the beak is separated 

 from the body by a deep constriction ; the body is usually oval, 

 the skin soft, occasionally with chitinous plates, which in some 

 species are finely striated ; a few hairs are always present, some- 

 times in the form of scales ; division between cephalothorax and 

 abdomen usually wanting ; legs generally short, five-jointed, 

 usually armed with two claws, between which there is a bunch of 

 hairs or a pectinate bristle. In some species the front legs 

 terminate in bristles, which appear, according to Banks to have a 

 tactile function ; in others the front legs are transformed into 

 clasping organs ; sometimes two eyes are present — one on each 

 side of the cephalothorax, but they are not often distinct ; 

 mandibles invariably long and needle-like, and fitted for 2:)iercing 

 tissues ; in one genus these organs are provided with two points. 



Family TETRANYCHID^. 



The Tetranychidie are popularly known as " Red Spiders " 

 and are familiar enough to most horticulturists ; or are 

 sometimes termed " spinning mites," from the fact tliat some of 

 the species spin fine silken threads. Some of the species have 

 followed their host plants, and hence have become widely 

 distributed, indeed cosmopolitan. In the present imperfect 

 state of our knowledge it is impossible to say how many species 

 (tccur in Australia, but several have certainly been introduced. 

 In addition to these there is little doubt but that some native 



'* Banks— ioc. tit., p. 18. 



