10 DEFINITION OF THE TERM INSECT. 



existence after they have laid their eggs a ; but the Crus- 

 tacea live longer, and lay more than once. 



The Arachnida will be found to diner 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 trachea? ; 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 antenna?, if we 

 admit the opinion on this head of MM. Latreille 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 Araneidce or 

 Spiders, their body seems to have no segments or incisure 

 but that which separates the abdomen from the trunk ; 

 and in the Scorpiotiidce 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 A?iaima, by 

 being built as it were upon a vertebral column, very ju- 

 diciously changed the denomination, which was indeed 

 improper, of " The Philosopher' £' two sub-kingdoms, into 



a The females of Dorthesia, however, a genus related to Coccus, are 

 said to survive laying their eggs. N. Diet. d'Hist. Nat. ix. 553. 



