EXTERNAL ANATOMY OF INSECTS. 653 
consideration of these organs in their perfect or last state; 
beginning with their number. Insects, properly so called, 
as I formerly observed *, in this state, including the an- 
terior 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”; this in some cases is said to 
be only a sexual distinction*. In Onitis, Phaneus, and 
some other Scarabaeidae, the arm has either none or a 
spurious tarsus or manus‘; which in the first of these 
genera is also a sexual character. From both these in- 
stances 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, Leptus, Astoma, Ocypete) 
have only stx legs; the rest, and the Arachnida in gene- 
ral, have eight ; in the Myriapods, Pollyxenus has twelve 
pairs; Scutigera has fifteen; the terrestrial Armadillones 
(A. vulgaris, &c.), sixteen; and the oceanic (A. ovalis), 
twenty ; the oriental Scolopendre, twenty-one ; Polydesmus 
has usually about thirty pairs ; Craspedosoma, fifty ; Geo- 
philus electricus at least sixty; in Iulus terrestris there 
are more than seventy; in I. sabulosus nearly one hun- 
dred ; in I. fuscus, 124; and in I. maximus, 134 pairs or 
268 single legs. But with respect to the Geophilz, Luli, 
&c., it is to be observed, that the number of pairs varies 
in different individuals; and the circumstance that has 
been before mentioned ¢, that these animals keep acqui- 
ring legs in their progress to the perfect state, instead 
" Vot. IL. p. 307. > De Geer i. t. xx. f. 11. 
“ Regne Animal. iii. 546. 4 Prats XXVII. Fre. 44, 45. 
¢ See above, p. 23. 
