Note 9 — Chapter III · THE PHYSIOLOGY OF THE CRAY­FISH—THE MECH­A­NISM BY WHICH THE LIV­ING OR­GAN­ISM AD­JUSTS IT­SELF TO SUR­ROUND­ING CON­DI­TIONS AND RE­PRO­DUCES IT­SELF.

It may be said that, strictly speaking, only those external bodies which are in direct contact with the organism do affect it—as the vibrating ether, in the case of luminous bodies; the vibrating air or water, in the case of sonorous bodies; odorous particles, in the case of odorous bodies: but I have preferred the ordinary phraseology to a pedantically accurate periphrasis.