386 NATURAL ARRANGEMENT OF INSECTS. 



usually united : their abdomen is not divided into seg- 

 ments : they have eight legs ; and their mouth is haus- 

 tellate or consisting of pieces, which form a sucking tube. 

 These comprise an extensive tribe of creatures, which 

 are excessively prolific, consisting also of many genera, 

 as Trombidium, Gamasus, Ixodes, Bddla, &c. The ma- 

 jority are very small, and occur every where beneath stones, 

 in moss, under the barks of trees, in flour, dried provi- 

 sions, old cheese, &c. ; others live as parasites upon the 

 skin or in the flesh of animals ; and some are said to be 

 the cause of certain loathsome diseases which affect 

 humanity, — the itch, for instance: they are found upon 

 other insects, and some have even been observed in the 

 eyes and brain of man. 



(350.) Our third division of the Aptera consists of 

 the jMyriapoda, or, as they are usually called, hundred 

 legs: they constitute the Chihgnatha and the ChUopoda, 

 and undergo a partial metamorphosis, which consists in 

 their acquiring, with every progressive moult, an addi- 

 tional number of segments and legs. The former have 

 short antenna? ; a convex cylindrical body, surrounded 

 by a hard integument ; neither maxillae nor palpi ; short 

 mandibles, andshort and slender legs. They occur usually 

 in humid situations, and beneath the bark of trees ; and 

 they feed upon both animal and vegetable productions. 

 They consist of Ghmeris, lulus, Polydesmus, &c. &c. 

 The ChUopoda have elongate antennae, a depressed body 

 covered with coriaceous plates, and legs of very variable 

 length : those with unequal legs constitute Scolopendra 

 proper, and its subdivisions, among which is the elec- 

 trical Geophilns. Those with equal legs have those 

 limbs very long, and form the genera Cermatia and 

 Scutigera. All of these run very fast ; they are carni- 

 vorous and nocturnal, and the majority occur beneath 

 stones, the bark of trees, and in humid loose earth. 

 The most of the exotic species are of large size, and are 

 said to be venomous. The rest, which do not undergo 

 a metamorphosis beyond a change of skin, and which 

 form the aberrant portions of the circle, if indeed they 

 belong here, consist of Leach's two orders, Thysanura 



