Economic entomology for the farmer and fruit-grower : and for use as a text-book in agricultural schools and colleges . gment bears a pair oflegs, which are themselves divided into joints or segments, andtheir structure will be described more in detail later on. This division into three distinct regions and the limitation tosix legs in the adult separate the insects from crustaceans, likelobsters, crabs, shrimps, and the like, and from the spiders ; noneof which have the head separate from the thorax, while all haveeight legs instead of six. An insect in the adult stage is there-fore a jointed
Economic entomology for the farmer and fruit-grower : and for use as a text-book in agricultural schools and colleges . gment bears a pair oflegs, which are themselves divided into joints or segments, andtheir structure will be described more in detail later on. This division into three distinct regions and the limitation tosix legs in the adult separate the insects from crustaceans, likelobsters, crabs, shrimps, and the like, and from the spiders ; noneof which have the head separate from the thorax, while all haveeight legs instead of six. An insect in the adult stage is there-fore a jointed animal, the rings, thirteen in number, separatedinto a head of one, a thorax of three, and an abdomen of ninesegments ; moving by means of three pairs of jointed legs. Somedifferences between larva and adult have been spoken of,and it has been indicated thereby that at different periods oftheir lives insects are unlike in appearance. This branch of thesubject is exceedingly interesting, and will be treated more fullyin Chapter VIII. It is only necessary to say here that, in speak- STRUCTURE AND CLASSIFICATION. 13. 14 .i^? ECOiVOMIC EXrOMOLOGY. ing of the difference between larva and adult, reference is particu-larly made to those forms in which the two stages are totallyunlike each other in appearance. Some of them resemble eachother throughout their entire life, and here the term nymphis often employed instead of larva. It remains to say a few words concerning the chitine, whichfonns so large a part of the outer skeleton or crust. This sub-stance is found in insects and in certain of^ the crustaceans, and is a flaky, horny, or shell-like material which may become veryhard, and is impenetrable to most liquidsnot absolutely corrosive in character. TheSection through insect importance of this fact it is necessary to crust, showing lavers of ? . i .^- r • ..• j chitine at .. the cellular rccogmze m our Selection of msecticides,layer or hypodermis at bccausc nothing that wc Ca
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectinsectp, bookyear1906
