Our insect friends and foes / by F. Martin Duncan.

  • F. Martin Duncan
Date:
1911
Catalogue details

Licence: In copyright

Credit: Our insect friends and foes / by F. Martin Duncan. Source: Wellcome Collection.

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    comprising the Scorpions, Spiders, Mites, and Ticks. The Insecta comprise a larger number of species than any other classes of the Arthropoda, numbering according to Dr. Sharp some 2,000,000 species, of which only about 250,000 have been described. Although the class is such an exten- sive one, it is characterized by a remarkable degree of anatomical uniformity. If we examine the body of any member of this great class of the true Insects, we shall find that it is segmented, bears a series of pairs of jointed appendages, and that the surface of the body and appendages is covered with a chitinous cuticle, which may be thin and soft as in the body of a caterpillar, or thick and hard as in the body of a beetle. This outward covering or exoskcletoiij composed of chitine, is intimately connected with the true skin beneath, the latter forming a deep, soft layer. The minute ducts of numerous small glands which are embedded in this layer of soft true skin, pass outwards to the exoskeleton, entering the base of the external hairs. It is the chitinous outer cuticle, which from time to time is cast, or moulted off during the growth and transformations of an insect. The segmented body of an insect is divisible into three well-defined regions, which are quite constant in their disposition, and comprise— (i) the head, formed by the union of the head- lobe of the embryo with some five segments, which are so closely united as to be indistin- guishable in the adult. It bears on its front lower (ventral) surface the mouth; upon its sides two
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