Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 STRUCTURE AND CLASSIFICATION. 49 which may or may not resemble the parent that laid it. Assum- ing that it does, it is without trace of wings. It grows apace, moults as often as necessary, and at last attains very distinct wing pads. It is now in the pupal stage, and with the next moult the wings become fully developed. It is then adult and fitted to reproduce its kind. This sort of metamorphosis is said to be incomplete, because there is
Economic entomology for the farmer and the fruit grower, and for use as a text-book in agricultural schools and colleges; economicentomolo00smit Year: 1906 STRUCTURE AND CLASSIFICATION. 49 which may or may not resemble the parent that laid it. Assum- ing that it does, it is without trace of wings. It grows apace, moults as often as necessary, and at last attains very distinct wing pads. It is now in the pupal stage, and with the next moult the wings become fully developed. It is then adult and fitted to reproduce its kind. This sort of metamorphosis is said to be incomplete, because there is no inactive stage, and because there is always a close resemblance in all stages. The larvae are quite usually termed nymphs, and differ from the adults only in size, in the absence of wings, and in the undeveloped sexual characters. A peculiarity of this method of growth or moulting is worthy of incidental mention. When the insect moults, it is not the outer Fig. 26. Moulting of a grasshopper.—a, nymph ready to change ; b, the skin split along the back and the adult emerging ; r, continues the process, and at d, the adult insect drying out. skin alone that is affected : all the most delicate mouth parts with their hairs and processes are cast and replaced by a new cover- ing ; the lining of a large proportion of the digestive system is shed, and the inner coat or surface of the tracheal tubes is renewed, so that practically the insect gets, in part, a new diges- tive system and a new breathing apparatus, every time it increases in size. The number of these moults varies in the different orders, and even in species of the same order. There may be as few as three or four, and there may be twenty or more. We can some- times modify the normal number by changing the circumstances under which the insects live. Thus, the larva of the common Dermestid found in museum cases normally moults four times 4
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