304 PHYSIOLOGICAL CONTROL IN ANIMALS 



Only limited information is available for the nerve net of cteno- 

 phores. On tactile stimulation, light appears under the combs, and 

 conductile pathways are likewise restricted to these areas. Nervous 

 transmission along the meridians is evidently unpolarized, since a 

 luminescent wave is capable of oral or aboral passage (Panceri, 

 1872b; Peters, 1905; Moore, 1924, 1926). With electrical stimulation, a 

 flash appears on each stimulus after the first. These flashes are of very 

 brief duration, about 0.2 second, and summate at frequencies above 

 5 per second (Fig. 4). Facilitation of response is also clearly recog- 

 nizable at slow frequencies of stimulation, the first few responses 

 increasing progressively in height to plateau level, after which fatigue 

 sets in. With repetitive stimulation, rhythmic flashing is also induced 

 {Beroe, Fig. 4). 



Fig. 4. Responses of the ctenophore Beroe to electrical stimulation (condenser 

 shocks). A, 2 shocks, 1-second interval. Note repetitive discharge on second 

 shock. B, 2-second burst at 7 per second. C, burst of 1. 1-second duration at 

 18 per second. D, burst of 3''/^ -second duration at 20 per second. E, 1-second 

 burst at 44 per second. Time scale, 1 per second. 



Luminescence in Animals with Central Nervous Systems 



As illustrative of nervous regulation in animals with a differentiated 

 central nervous system, I shall refer to two groups with which I have 

 had personal experience. These will provide examples of intracellular 

 luminescence at invertebrate and vertebrate levels. 



Polynoids 



In polynoid or scale worms, flashes are produced by the dorsal 

 elytra under appropriate stimulation. The photocytes involved are 

 innervated by fibers which emerge from a ganglion in the center of 

 the elytrum. The normal response to a single shock is a series of 



