Among insects, for example, the location of the antennae has no distinctive value because it is not in correlation with any of the main internal structures; the form of the lower jaw, on the other hand, can play a leading role in arranging them according to their resemblances and differences; for it is connected with the insect's food and digestion, and thus with its essential functions: 'the organs of mastication must be related to those of digestion, consequently to the whole mode of life, and consequently to the whole organic structure'.