24 DEFINITION OF THE TERM INSECT. 



are affixed only six legs 8 , proves that even this circum- 

 stance possesses no weight when set against the organi- 

 zation. If it was a difference in this respect, that proved 

 the Crustacea classically distinct from Insecta — that like- 

 wise was the principal reason for the separation also of 

 the Arachnida — it seems to follow that it ought also to 

 furnish an argument equally cogent for considering the 

 Trachean Arachnida, as well as the Myriapoda, distinct 

 from the Pulmonary. 



Another difference between the tribes in question is 

 that of their metamorphosis ; and this appears to have 

 had great weight with Lamarck, inducing him to include 

 in his Arachnida, not only the Tracheans and Myriapods, 

 but even the apterous Hexapods, except Pidex, or the 

 Anoplura and Thysanura of modern authors- But the 

 metamorphosis alone, unless supported by the internal 

 organization, will I think scarcely be deemed a sufficient 

 reason for separating from each other tribes agreeing in 

 that respect, and placing them with others with which 

 they disagree. The metamorphosis in some of the Hexr 

 apods (Lepidoptera) consists in the loss of legs, the ac- 

 quisition of wings, a great change in the oral organs and 

 in the general form; in others (some Coleoptera), in the 

 acquisition only of wings and a change of shape, the oral 

 organs remaining much the same; in others again (Cur- 

 cidio L.), in the acquisition of six legs and wings and a 

 change of form ; in the flea, in the acquisition of six 

 legs and a change of form only ; in the Qrthoptera, He- 

 miptera, &c. in the mere acquisition of wings ; . in the 

 Libellulidce, in the loss of the mask that covers the mouth 

 and the acquisition of wings ; in the Diptera, in the ao- 



* Dufour ubi supra. Hor. Entoniolos. 382, 



