INSECTS 



181 



f.w. 



Class IV. Insects. 



The word insect is popularly but mistakenly used of all sorts of small 

 creatures not only of Flies, Moths, and Butterflies, but also of Spiders, Centi- 

 pedes, and others. It is necessary therefore to define as briefly as possible 

 the kind of creature to which the term is properly applied. First, its deriva- 

 tion teaches us something. It comes from the Latin " to cut into," and 

 therefore refers to the three distinct divisions of a true insect's body head, 

 thorax, and abdomen which are often separated from each other by an 

 exceedingly small neck and waist. 

 No such threefold division character- 

 izes the Spider or the Centipede. 

 Second, all insects reach their full 

 adult stage through certain changes 

 or metamorphoses from the egg to 

 the grub, larva, or caterpillar. This, 

 when full grown, changes to a pupa or 

 chrysalis, and from this the perfect 

 insect, or imago, finally emerges. The 

 larvae are usually very voracious 

 feeders, and as they grow, change or 

 moult their skins several times; but 

 the pupae, as a rule, are inactive, eat- 

 ing nothing, and generally encased in 

 cocoon or hidden underground, or in 

 some other place of concealment. 

 During this period a remarkable 

 change gradually takes place, the 



organs of the larval form disappear- A Beetle viewed from below as an example 



ing, and those of the perfect insect [ I nsecta: * single pair of antenna?; abd, 

 -, f j abdomen; f.w., fore-wing; gn l , gn z , gn 3 , the 



three pairs of gnathites; h.w., hind-wing; h, 



The perfect insect has always three head ; *> walking legs ; th, thorax, 

 pairs of legs, and generally two pairs 



of wings, though many, such as flies and gnats, have but one pair ; and some, 

 like fleas, have none developed for flying. All insects breathe by means of 

 air-tubes, called tracheae, opening along the sides of the abdomen into stig- 

 mata, or spiracles very minute " little mouths " through which the air enters. 

 They also possess two sensitive organs of touch the antennae, or feelers, which 

 are of very varied form, and by which it is probable they hear, smell, and touch. 

 They live by gnawing or sucking in the former case having mouths specially 

 formed for the purpose ; in the latter having a proboscis or trunk (often called 

 the tongue) running out from the lower lip. Again, most insects have two 

 large eyes, consisting of a vast number of small lenses grouped together, thus 



