EXTERNAL ANATOMY OF INSECTS. 461 
underneath with a double row of stout teeth; and the 
terminal one is more solid and harder, in the form of a 
very sharp crooked claw, which in inaction is folded on 
the first joint between the teeth. Under its extremity on 
the outside is a minute orifice, destined to transmit a ve- 
nomous fluid; which is conducted there by an internal 
canal from the base of the first joint, where is the poison- 
bag. In the scorpion and harvest-man (Phalangium) 
the mandible consists of two joints terminated by a chela 
or double claw, the exterior one being moveable>.— 
M. Latreille, as has been before observed, regards these 
not as representatives of the mandibles of hexapods, but 
as replacing the interior pair of antennze, in the situation 
of which they are precisely placed, of the Crustacea‘ : 
and M. Savigny is of opinion that the Arachnida may in 
some sort be defined as Crustacea without a head, and 
with twelve legs, of which the two first pair are converted 
into mandibles and maxille’. From the situation of the 
organs in question, the first of these opinions seems pre- 
ferable; but the conversion of the legs in other cases, at 
least the core, into organs of manducation, gives some 
weight to the last. With regard to their wse, it is said 
to be to retain the insect which the animal has seized, 
and to facilitate the compression which the maxillze exer- 
cise upon it for the extraction of the nutritive matter‘. 
If this be correct, 27 thzs respect the mandibles may be 
said to represent the mazille of the mandibulate hexa- 
pods; and, vice versa, the sciatic maxille, as they have 
a N. Dict. d@ Hist. Nat. ii. 275—. Piate VII. Fie. 10. ec’. 
» De Geer ¢. xl. fi 4.4.x. f.7, 8. * See above, p. 18, 30. 
4 Savigny Anim. sans Vertebr. I. i. 62. 
e N. Dict. d’ Hist. Nat. ii. 277. 
