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Rh and use from the mouth of gnawing insects, it is found to be composed of the same or corresponding parts, with the exception of the palpi, which are quite obsolete. These parts, however, have, of course, undergone great modifications, to such a degree, indeed, that it is exceedingly difficult to recognise them. It is only from their insertion and position relatively to each other, that any agreement can be inferred; and, at most, the oral organs of suctorial species can only be considered as analogous to or representative of the parts of a mouth formed for mastication. There is reason to believe that some of the ingenious observers, who have turned their attention to this subject, have carried their views rather too far, from a wish to demonstrate a certain uniformity of organisation among different tribes—an interesting inquiry, but one which requires to be pursued with great caution, as the fancy is so apt to lead us astray. At all events, we have been often led from this cause to the application of names, which, however significant as originally used, becomes quite inappropriate in their present extended acceptation. The term mandibles, for example, is sufficiently descriptive of the gnawing organs of the mandibulata, but is wholly unmeaning when applied to a slender filet composing a portion of a tube, in which both the form and the function are completely changed. The rostrum, when not employed, is bent beneath the breast, to which it is closely applied, passing between the legs. It consists of four joints, generally distinctly marked, of a cylindrical form, or tapering