680 EXTERNAL ANATOMY OF INSECTS. 



1:1:1; in Atia Latreille, a kind of ant a , 1:0:0. In the 

 Diptera it is often difficult to distinguish the spurs from 

 the spines ; but the number most universal is, I think, 

 2:2:2; in Tipida it is 1:2:2; in the Tabanidce 0:2:0; 

 and in Culex, Limonia, &c, there are none. Amongst 

 the insects with more than six legs, most commonly the 

 tibiae have no spurs ; but in the Araneidce each is armed 

 with two, a circumstance which also distinguishes the 

 corresponding joint of the ])edipalpi. 



These little organs inosculate each in an appropriate 

 socket of the end, or in many cases of the middle of the 

 tibia; and that part of their head or base that is received 

 by it, is often constricted for the purpose : from hence 

 it follows that they are capable of some degree of motion, 

 but in some insects, as those on the four posterior legs of 

 Scarabceus sacer and its more immediate affinities, and 

 those at the end of the cubit of Gryllotalpa, they are im- 

 moveable, and appear almost processes of the joint to 

 which they belong. They are commonly sharp, of a 

 sujjtriquetrous figure, with the lower side flat: where 

 there are two, the outer one is usually the longest ; and 

 in general the spurs on the hind legs are longer than 

 those on the four anterior : but there are exceptions — 

 thus, in Acanthopus Latr. the intermediate spurs are the 

 longest; and in Cicindela the anterior are longer than 

 the former ; in Blaps mortisaga those on all the legs are 

 nearly equal in length. They vary sometimes m shape— 

 those on the middle of the cubit of many Lepidoptera, 



3 Most of Latreille's genera cf ants are confirmed by differences 

 nx their spurs. Thus Formica is 1 : I : 1 ; Ponera 1:2:2 with the 

 internal intermediate one pectinated: Myrrnka 1:2:2 with all sym- 

 metrical, &c. 



