ad to add some further explanation relating to the physiological functions of its respective parts besides the incidental notices on this head already given. The food to be transmitted through its various chambers, if of a solid substance, undergoes a process of mastication by the oral instruments; but this process is not in all cases equally complete. Many predaceous kinds, particularly among the Coleoptera, masticate their food very imperfectly, merely dividing it into such pieces as admit of being swallowed. Further mastication is doubtless rendered unnecessary in their case by the presence of a gizzard where the trituration is afterwards perfected. Raptorious species destitute of the organ just named, (such as Dragon-flies) thoroughly comminute their food before swallowing it. Solid vegetable matters are of course always considerably reduced in the mouth; but those insects which feed on green leaves, particularly the caterpillars of Lepidoptera, swallow the small pieces they detach almost or entirely unchanged. In suctorial insects, as well as those which have been termed Lappers (the Stag-beetle is an example), mastication obviously becomes superfluous.
But it is not the mechanical action of the trophi (as the oral organs are sometimes called) alone that the food is subjected to in the mouth; it is here that it mingles with the secretions of the salivary vessels. These secretions consist of a whitish, frequently a purely hyaline fluid, said to be of an alkaline nature. The intermixture, to adopt Burmeister's words, has
