Economic entomology for the farmer and fruit-grower [microform] : and for use as a text-book in agricultural schools and colleges economicentomolo00insmit Year: 1896 STRUCTURE AND CLASSIFICATION. 31 Fig modified for special purposes ; as in some of the piercing insects like bugs or the mosquitoes, where an irritant poison is secreted, or in certain beetles, where the saliva has both a staining' and a burning effect upon the skin, or in many larvae, where the se- cretion forms a silk when hardened by ex- posure to the air. The anal glands may be similarly modified, but much more rarely than t
Economic entomology for the farmer and fruit-grower [microform] : and for use as a text-book in agricultural schools and colleges economicentomolo00insmit Year: 1896 STRUCTURE AND CLASSIFICATION. 31 Fig modified for special purposes ; as in some of the piercing insects like bugs or the mosquitoes, where an irritant poison is secreted, or in certain beetles, where the saliva has both a staining' and a burning effect upon the skin, or in many larvae, where the se- cretion forms a silk when hardened by ex- posure to the air. The anal glands may be similarly modified, but much more rarely than those at the anterior end of the body. In the 'Bombardier beetle' their secretion volatilizes suddenly when expelled into the air, and forms a blue smoke, like the discharge from a small cannon. In Hymenoptera, including bees and wasps, the secretion is poisonous, and accessory to the functions of the sting. More rarely a silk is produced from these glands. Taken altogether, the digestive system varies greatly in length, being sometimes a straight tube only, the various portions very incompletely divided off. In other cases it is quite complex, coiled upon itself, the parts well defined, and the sys- tem as a whole two or three times the length of the entire insect, different kinds of structure being found in the various parts. The figures given herewith illustrate some of these differences. Salivary gland of the cat- erpillar of Melitha ceto. In the sucking or haustellate type the modified for siik spinning: essential structure of the alimentary canal mandible of the same, and the differentiation of the parts are much the same. There is, however, a great reduction in the size of the gizzard, which is very often entirely wanting. If present, the armature is reduced to a mere ridging, or a slight, irregular thickening of the walls of the posterior end of the crop. In the Lepidoptera there is often a peculiar accessory pouch, which seems to serve the purpose of a storage reservoir
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