10 DEFINITION OF THE TERM INSECT. 
their existence after they have laid their eggs*; but the 
Crustacea live longer, and lay more than once. 
The Arachnida will be found to differ from insects 
more widely than even the Crustacea. ‘They agree in 
their jointed legs and palpi; immoveable eyes; and in 
being covered with a coriaceous or corneous integument: 
but they differ in having a system of circulation; gills 
instead of trachez; their organs of generation double ; 
and the females lay more than once in their lives. Their 
head also is not distinct from the trunk as in insects ; 
they have no compound eyes; and their antenne, if we 
admit the opinion on this head of MM. Latreiile and 
Treviranus, that they have representatives of these or- 
gans, differ totally in structure, situation, and use, from 
those of the great body of insects. In the Araneide or 
Spiders, their body seems to have no segments or incisure 
but that which separates the abdomen from the trunk ; 
and in the Scorpionide they are observable only in the 
abdomen. Other particulars might be enumerated in 
which these two classes differ from insects; but these will 
be sufficient to convince you that Aristotle and MM. Cu- 
vier and Lamarck were justified in separating them. 
The two last-mentioned authors made further improve- 
ments in Zoology. The latter, from the consideration of 
the general structure of animals, perceiving that Aristo- 
tle’s Enaima were distinguished from his Anaima, by 
being built as it were upon a vertebral column, very ju- 
diciously changed the denomination, which was indeed 
improper, of “The Philosopher’s” two sub-kingdoms, into 
* The females of Dorthesia, however, a genus related to Coccus, are 
said to survive laying their eggs. N. Dict. d’ Hist. Nat. ix. 553. 
