EXTERNAL ANATOMY OF INSECTS. 679 
Diptera it is often difficult to distinguish the spurs from 
the spines; but the number most universal is, I think, 
2:2:2;in Tipulait is 1:2:2; inthe Tabanide 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 Araneide each is armed 
with ¢wo, a circumstance which also distinguishes the 
corresponding joint of the pedipalpi. 
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 
Scarabeus sacer and its more immediate affinities, and 
those at the end of the cubit of Gryllotalpa, they are 
immoyeable, and appear almost processes of the joint 
to which they belong. They are commonly sharp, of 
a subtriquetrous 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 the intermediate spurs are the 
longest; and in Ciczndela the anterior are longer than 
the former ; in Blaps mortisaga those on all the legs are 
nearly equal in length. They vary sometimes in shape— 
those on the middle of the cubit of many Lepidoptera, 
which may be regarded as a kind of thumb’, are of a 
lanceolate shape ; in Meloe the external posterior one is 
in their spurs, Thus Formica is 1:1:1; Ponera 1: 2:2 with the 
internal intermediate one pectinated: Myrmica 1: 2: 2 with all sym- 
metrical, &c. ° Pirate XXVU. Fie. 29, v'’. 
