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82 detected. Not rarely, however, they are pretty conspicuous, consisting of four or five joints in the majority of beetles, and of two or three in caterpillars. The joints are frequently contractile within each other, so that the antennæ can be protruded or withdrawn at the pleasure of the animal. The head of larvæ is usually of a harder substance than the rest of the body, and in that case is commonly of a triangular or orbicular shape; but its covering among the diptera is soft and membranous, from which results the singular anomaly that it is capable of dilatation and contraction, and therefore of assuming any form the insect may desire. The remarkable spines that arm the heads of many foreign caterpillars, have been already mentioned. On the various and numerous appendages of larvæ, whether serving for respiration, ornament, or defence, it is unnecessary to enlarge in this place, as it would only be anticipating what can be more appropriately introduced hereafter. Their anatomy will be considered conjointly with that of the perfect insects. But there are other interesting features in their history, to which it will be most convenient to advert in this place, namely, their growth, moulting, and preparations for entering upon the pupal or penultimate state. The growth of larvæ is in most cases rapid. The whole structure of the animal, indeed, indicates provision for its speedy increase in size. The