been already explained, and further details will be given hereafter.
Whenever the larvæ are provided with oral organs formed for suction, the same conformation obtains in the prefect insect; but suctorial species are often produced from masticating larvæ. In the former case the nature of the food scarcely varies in the whole course of the animal's existence; in the latter it must necessarily be quite dissimilar. The various parts of the mouth, as well as other appendages of the head, are analogous in form and function to those that exist in the imago. An upper and under lip, mandibles and maxillæ, and from two to six palpi can be distinguished; antennæ and eyes (the latter generally of the simple construction,) are likewise present, in far the greater number of cases. The mandibles vary in form and consistency according to the nature of the substances upon which they are designed to act: in many carnivorous tribes they are long and curved; and in Dytiscus, Hemerobius and Myrmelion, they have another and a singular function superadded to their ordinary uses: they are perforated throughout their whole length, and thus form a tube through which the animal sucks the juices of the prey which it has secured by their means. Among many Diptera, the mandibles serve as instruments of motion; the larva fixing its posterior part to the plane of position, and then stretching its body in advance, seizes some point of support with its jaws, and by their aid easily drags the body
