654- EXTERNAL ANATOMY OF INSECTS. 



the water, and by which also they perform various ope- 

 rations connected with their economy a . In treating of 

 them we should consider their number; kind; substance; 

 articulation with the trunk; position; proportions; cloth- 

 ing; composition; folding; and motions. 



1. Number. Having before very fully explained to you 

 the number and kind of the legs of insects in their pre- 

 paratory states 5 , I shall now confine myself to the con- 

 sideration of these organs in their perfect or last state ; 

 beginning with their number. Insects, properly so call- 

 ed, as I formerly observed , in this state, including the 

 anterior pair or arms, have only six legs, none exceeding 

 or falling short of this number ; but in several of the 

 Diurnal Lepidoptera (Vanessa, &c.) the anterior pair 

 are spurious, or at least not used as legs, the tarsi having 

 neither joints nor claws d ; this in some cases is said to be 

 only a sexual distinction e . In Onitis, Phanceus, and some 

 other Scarabceidce M. c Ij., the arm has either none or a spu- 

 rious tarsus or mantis f ; which in the first of these genera 

 is also a sexual character. From both these instances 

 we see that walking is only a secondary use of fore- 

 legs in the insect tribes. Besides insects proper, a whole 

 tribe of mites (Caris Latr., Leptus Latr., Astoma Latr., 

 Ocypete Leach) have only six legs; the rest, and the 

 Arachnida in general, have eight; in the Myriapods, 

 Polly xenus has twelve pairs; Scutigera has fifteen ; the 

 terrestrial Glomerides (G. Armadillo, &c.) sixteen; and 

 the oceanic (G. ovalis) twenty; the oriental Scolopendrtz 

 Leach, twenty-one; Polydesmus has usually about thirty 



a See above, p. 546—. h Ibid. 131 . 



c Vol. II. p. 307. * De Geer i. t. xx. /. 1 1. 



e Regne Animal, iii. 546. * Plate XXVII. Fig. 44,45. 



