J. A. C. NICOL 309 



tion of F. Haxo), and Noctihica (contradictory observations; see 

 Harv^ey, 1952), pennatulids, possibly Pdagia and generally in cteno- 

 phores (Peters, 1905; Moore, 1924; Heymans and Moore, 1924; 

 Harvey, 1952). 



Primary inhibition of this kind effects conservation of photogenic 

 material in dayhght, and the material is reserved for use in darkness. 

 Su(?h a mechanism presents functional simplicity and advantages in 

 organisms with restricted and common modes of regulation of diverse 



TIME Ml N 



Fig. 6. Course of reco\ery of luminescence in Renilla when transferred from 

 liglit to darkness. Ordinate: intensity of response evoked by a burst of shocks. 

 Abscissa, time in minutes after transferring animal from light to darkness. 



responses. In Renilla, for example, we find that luminescence attains 

 full intensity only after 1 to 2 hours sojourn in the dark (Fig. 6). 

 Now, tactile stimulation in this animal evokes both movement (con- 

 traction) and luminescence, and it is highly probable that all these 

 responses are controlled by the same nerve net. Nevertheless, the 

 dependence of luminescence on previous dark exposure ensures that 

 the luminescent response is reserved for times of darkness, even 

 though photocytes and muscle fibers are reached by efferent impulses 

 from tactile receptors at all times. 



Reflex inhibition of luminescence by daylight through photosensi- 

 tive receptors might be expected, but no instances appear to have 

 been recorded. Certainly, many animals, with differentiated central 

 nervous systems, will luminesce when reflexly stimulated in daylight, 

 e.g., polynoids, Chaetoptenis, Amphiura. There are some suggestive 



