The Motor Mechanism of the Insect Leg

IN view of the number of papers that have appeared in recent years on* the neuromuscular systems of various groups of animals, it is somewhat surprising that no attempt has been made to clarify the position in regard to the insects. There can be no doubt that a particular interest attaches to this group from the standpoint of comparative physiology. As the most highly developed members of the Arthropod phylum they represent the end of an important evolutionary line; as successful colonists of the land they have been faced with some of the same difficulties that confronted the higher Vertebrates, and in many cases have found different solutions. Nowhere is this more obvious than in the problems of locomotion. On the sensory side we find the proprioceptive system of insects highly developed and differing radically from that of the Vertebrate (Pringle, 1938 a, b), and the present paper will bring out further differences in the motor mechanism. Perhaps we should regard as the most interesting feature of the whole comparison the very fact which has served to mask the inherent differences: the extraordinary outward similarity of the locomotory mechanisms in the two groups; a similarity imposed on essentially different animals by the exigencies of a common environment.