Organs of Invertebrate Animals. 43 



form is such as to make it certain that they are not 

 special organs, but merely modifications of the foot-jaws 

 and of the true and false feet behind them. 



The trophi or oral appendages of a mandibulate 

 insect consist of two pairs of lateral jaws, the upper 

 being the mandibles, the under the maxillae, which work 

 from side to side like the true jaws of the Crustacea, 

 and of two lips, the upper one called the labrum, and 

 the under one the labium, which act in an up-and- 

 down direction like the jaws of a vertebrate animal. 

 The maxillae carry palps, and in other respects are not 

 unlike the maxillae of the Crustacea: the mandibles 

 are more simple in form, stronger, and palpless. In 

 some instances, the maxillary palps " besides their 

 sensitive and selective offices, serve also to seize and 

 steady the alimentary substances whilst these are being 

 divided by the mandibles and maxillae, representing, in 

 fact, a third pair of lateral jaws." The labium has 

 usually a pair of palps, and, in addition, within the 

 mouth, a process called the tongue, which is particu- 

 larly developed in the dragon-fly and many beetles. In 

 the haustellate insects the mouth is still made up of the 

 same parts. In the bee tribe the mandibles are strong 

 cutting organs very like those of the mandibulate beetle, 

 but the maxillae and labium, which go together to form 

 the proboscis, are very much altered, especially the 

 labium. The maxillae have still their palps, and so has 

 the labium ; the latter organ may indeed have an extra 

 pair. In the hemiptera mandibles and maxillae alike 

 are attenuated and prolonged into lancet-shaped organs, 

 for which the elongated labium serves as a sheath : and the 

 palps have disappeared. And so also in the diptera, with 

 this difference that the labrum is also lancet-like, and that 

 the sheath formed by the labium is terminated by two 



