In favour of seeing in the lateral trunks and their branches a vascular system, is the contractility of the former, and the fact of the intrusion of the latter into the epidermis, matched among the Oligochaeta, where undoubted blood capillaries perforate the epidermis.
The manifestations of contractility by muscle are various in mode.
Another mode of manifestation of contractility by muscles is the rhythmic. A tendency to rhythmic contraction seems discoverable in almost all muscles.
The inference is that the "fatigue substances" generated in the muscle fibres in the course of their prolonged contraction injure and paralyse the motor end plates, which are places of synapsis between nerve cell and muscle cell, even earlier than they harm the contractility of the muscle fibres themselves.
Recent data has revealed that stretch injury may enhance contractility but also increase the sensitivity of the vessel to agents which release nitric oxide.