J. A. C. NICOL 315 



known, however, of animals in which the luminescent response can be 

 quite localized, e.g., in teleosts where separate photophores or groups 

 of photophores light up independently of others. Among lower animals 

 I cite Cliaetopterus, in which the response can be caused to invade 

 an increasingly greater number of segments by increasing frequency 

 and number of stimuli. Moreover, the response spreads with greater 

 facility posteriorly than anteriorly. Here we have instances in which 

 the locus of response is controlled by the central nervous system, by 

 functional polarization, facilitation, and possibly by central representa- 

 tion of peripheral fields in higher forms (teleosts and cephalopods). 



Control of Spectral Emission 



There are a number of animals possessing several differently colored 

 photophores, capable of emitting light of different colors, e.g., the 

 beetle Phrixothrix and the squid Thaumatolampas. In some of these 

 animals the differently colored photophores can respond indepen- 

 dently of each other, thus providing light of different colors according 

 to the stimulus. The possibility also exists, moreover, in certain 

 animals in which the light is controlled by chromatophores, that these 

 organelles may influence the color of the light emitted, according to 

 their condition and pigment characteristics. 



Conclusions 



Regulation of luminescence must be related to neuro-effector con- 

 trol in general, and in fact, involves control of four different mecha- 

 nisms, viz., glandular secretion, muscular contraction, chromatophore 

 movement, and intracellular photogeny. Most recent work on neuro- 

 effector, and in particular, neuromuscular, control is being carried out 

 at the molecular level, in an attempt to discover the details of trans- 

 mitter action. Regulation at the interface between nerve fibers and 

 light organs is liable to display great variation in different systems 

 and in different animals. Accepting differences in transmitter action, 

 we may, in the last analysis, discover much uniformity in patterns 

 of energy release effecting the photogenic response. 



In those animals which hitherto have been studied, overall regula- 

 tion of luminescence is achieved by transmission of an excitatory state, 

 either across the surface of the cell (protozoa, eggs), or through 



