308 PHYSIOLOGICAL CONTROL IN ANIMALS 



or dispersion, intensify or weaken emission without occluding it 

 entirely. The light of Secutor and Gazza is said to increase suddenly in 

 brilliance when the fish are strongly stimulated (Haneda, 1950). 

 There is still some uncertainty about the mode of regulation obtain- 

 ing in teleost chromatophores, but it is at least certain that pigment 

 concentration is achieved by sympathetic stimulation and administra- 

 tion of adrenaline, and that the chromatophores are innervated by the 

 sympathetic nervous system (Parker, 1943, 1948). Tactile stimulation 

 is known to cause chromatophore concentration and blanching in some 

 fish and is possibly a significant factor in transient intensification of 

 light emission in fish with bacterial light organs (Osborn, 1939). 



Chromatophores, overlying light organs, also control emission in 

 cephalopods. In these animals, however, the chromatophores are 

 actuated by muscle fibers, which expand the pigment cell when they 

 contract, and allow it to contract when they relax. The appearance 

 of light on concentration of chromatophores and occlusion on expan- 

 sion of chromatophores have been described in Watosenio sclntiUans. 

 As Harvey (1952) has pointed out, direct control of light production 

 may also be involved in these screened photophores. 



Modes of Direct Control of Photogeny 



The basic problem in control is turning the light on and off. More- 

 over, luminescence is a response with certain characteristics and 

 parameters which, theoretically, can be varied in five ways, viz., in 

 quality (spectral emission), intensity, duration, spatial distribution, 

 and frequency or repetition. In actuality, we find that control of one 

 or more of these variables is exercised by animals. 



Inhibition 



Perhaps the simplest and most direct form of control consists of 

 inhibition of luminescence by illumination. This can be exercised in 

 either of two ways: by direct inhibition of photogenic material, or by 

 reflex inhibition in the sensori-neural system. It is probably significant 

 that nearly all instances of direct inhibition of photogenic material or 

 photocytes are confined to the Protozoa, Coelenterates, and Cteno- 

 phores, animals either lacking a nervous system or provided with a 

 nerve net. It is variously reported for Gomjaidax (personal observa- 



