18 DEFINITION OF THE TERM INSECT. 
is subject when young ; legs most commonly reduced to six*. 
Putmonary ARACHNIDA: An organ for circulation. 
Gills for respiration on each side of the abdomen under- 
neath. Sexual organs double. From six to eight simple 
eyes. Two mandibuliform claws terminated by one or two 
Jingers, one of which is moveable. Two maxilla bearing 
a five-jointed feeler. An upper lip, a tongue, and four 
pairs of legs. 'TRAcHEAN ARAcHNIDA: Heart replaced 
by a simple dorsal vessel. Respiration by radiating 
trachese usually receiving the air by two abdominal or 
thoracic spiracles. Sexual organs single. Eyes never 
more than four, mostly two. Mouth forming a siphon>.” 
Under this head he observes—‘Of all these charac- 
ters, the most easy to seize and the most certain would 
doubtless be, if there were no mistake in it, that of the 
absence of antenne; but later and comparative re- 
searches, confirmed by analogy, have convinced me, that 
these organs, under particular modifications it is true, 
and which have misled the attention of naturalists, do 
exist®:” and he supposes, from the situation and direc- 
tion of the mandibles of the Arachnida, corresponding 
with that of the intermediate pair of antenne in Crustacea, 
that they really represent the latter organs. If this sup- 
position be admitted, their use is wholly changed; the 
palpi, in fact, executing the functions of antennze, which 
probably induced Treviranus to call them Fiihlhirner 
(Feeling-horns). Perhaps these last may be regarded 
as in some sort representing the external antenneze of the 
Crustacea? With regard to Insecta, their antennze seem 
* Des Rapports Généraux Sc. des Anim. Invertebr. Ann. du Mus. 
1821. 119—. > Fam. Nat. du Régne Animal, 309, 317. 
© Des Rapports Généraua, §c. ubi supra. 
