Miscellaneous. 483 Determination of the Directing Element in tJie Jaws of Insects. By M. Joannes Chatin. In a previous series of researches, the results of which I have submitted to the judgment of the Academy *, I have studied the variations which the jaws can present, not only in their ensemhle, but in the parts of which they consist, wheii studied in boring-insects. For the purposes of such investigations these repre-sent the fundamental types ; remaining always near to its initial state, the jaw permits of the accurate recognition of the smallest details as to the development, relations, &c. of its different parts. Highly instructive for all that relates to the descriptive anatomy of the organ though the boring-insects (" insectes broyeurs ") are, they become insufficient when it has to be considered from the point of view of philosophic anatomy. Among other questions in this connexion there is one which has been generally left in the shade. The theory of Savigny has traced in its broad lines the series of transformations which the jaw undergoes in order to adapt itself to the varying mode of life of insects. But what is the role to be assigned to the different parts of the jaw in its numerous functional adaptations ? Ought they to play an equal part, or should one of the parts be pre-eminent? should it reduce the others to the position of satellites or assert itself as the centre of the curious processes which so strangely metamorphose the organ ? After a minute analysis, the question cannot be elucidated except by varying within wide limits the types on which it is proposed to determine which is the directing element of the jaw. It is easily settled when one passes from the Borers to the Hymeno-ptera. According to a too widely spread opinion, their jaw would always take on the character which it presents in the Apidte, in which its appearance differs profoundly from that in the Borers. There is nothing so baseless as this generalization ; in reality the form proper to the Borers reappears in several genera ( Vespa, Micro-gaster, &c.). The base of the organ is formed by a submaxilla, above which rises the maxilla, iiguring as the central limb of the jaw ; on its upper part it displays three appendages, among which the palp is far the most developed, the two others (galea and inter-maxilla) appearing to be still secondary. In Gonatopus, Xyphidrina, and Bracon it is seen that the galea increases progressively, at the same time that the intermaxilla approaches it more and more closely. In the genus Perilampus the formation of a mixed galoo-intor-maxillary plate may be seen. This is definitely constituted in Cepluis and Megacliile, much elongated, absorbing, so to speak, the intermaxilla ; the galea is transformed into a powerful blade, which becomes henceforth the principal part of the jaw. Here, then, is an organ completely modified, in no way resembling what it was in the Borers, tending, on the contrary, to the form presented by the Suckers, such as the Lepidoptera &c. I could pass at once to the examination of these latter, but it * ' Comptes Eeudus,' 1879-1887, and ' Concours pour le Grand Prix des Sciences physiiques,' 1885.
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