INTKODUCTION. 



I.— THE CLASS INSECTA. 



As the Lepidoptera (Butterflies and Moths) are an Order of the Class 

 Insecta or true Insects, a few words are requisite to indicate the 

 structure of these animals. 



The entire class is associated with three others, viz., the Arachnida 

 (Spiders, Scorpions, &c.), the Myriopoda (Centipedes, Millipedes, &c.), 

 and the Crustacea (Crabs, Lobsters, &c.), to form the great sub- 

 kingdom ARTHROPODA. This immense assemblage is characterised 

 by the body consisting of a series of rings or segments (somites) bearing 

 hollow jointed limbs ; and by the integument being so hardened and 

 solidified by the peculiar deposit chitine, as to constitute a more or less 

 rigid external skeleton to which the muscles are attached. The rings 

 or segments of the body succeeding those which unite to form the head 

 do not, as in the higher members of the sub-kingdom Vermes, present 

 a repetition of the same structure throughout their series, but tend 

 with more or less distinctness to form two separate groups or regions 

 to which special organs and functions are allotted. These two unequal 

 sets or groups of segments are respectively termed thorax (the anterior) 

 and abdomen (the posterior) ; and, speaking generally, the organs and 

 functions of locomotion may be said to reside in the former, and those 

 of nutrition and reproduction in the latter. 



The Crustacea are separated from the rest of the Arthropoda by a 

 respiratory system working by gills (hranchice), adapted to their aquatic 

 life ; while all Insects, Myriopods, and Arachnids are alike in direct 

 aerial respiration by breathing-tubes (trachcm) traversing the body 

 and opening on its exterior by stigmata, — or (in the case of certain 

 Arachnids only) by pulmonary sacs. Associated with this important 

 distinction there are others of much note in external structure. Thus, 

 the Crustacea have two pairs of anfennm, — other Arthropods but one 

 pair ; in the former there is a second pair of inferior jaws (inaxillw) 

 functionally active, — but these in the other classes are united to form 

 the under- lip (labium) ; the abdominal limbs of Crustaceans have no 

 representatives in adult Insects or Spiders (though homologous append- 

 VOL. I. A 



