PHOTIC SENSITIVITY OF BALANOGLOSSUS 215 



interfered with This is, of itself, insufficient proof of the sepa- 

 rateness of the sensory organs concerned in the reception of 

 photic stimulation, but it does show that photic irritability de- 

 pends upon a process distinct from that implicated in the other 

 modes of stimulation. 



The general surface of the balanoglossids which I have, em- 

 ployed is also sensitive to light, as previously stated, although 

 this sensivity is much lower than that of the proboscis-tip. 

 Local movements begin rather promptly when bright light is 

 thrown upon portions of the animal; and even when an animal 

 is photically so exhausted that orientation no longer results, 

 there is still some increase in movement when the luminous 

 intensity is suddenly increased. 



Light has also another effect on Ptychodera, and on Glosso- 

 balanus. It is known that sunlight inhibits the production of 

 light by certain animals. One such case was carefully studied 

 by Peters ('05), who showed that the phosphoresence of the 

 ctenophore Mnemiopsis was inhibited by sunlight, although 

 its recovery of luminous powers in the dark was accelerated if the 

 animal was simultaneously agitated by mechanical means. 



All the Enteropneusta with which I am acquainted can pro- 

 duce a vivid greenish light, from every portion of the body 

 save the gills. When placed in a dark room during daylight 

 hours, they do not exhibit their phosphorescence in response 

 to mechanical stimulations of various kinds. And even at 

 night, after they have been in darkness for some time, five 

 minutes' illumination by the relatively feeble light from a 

 twenty-five watt tungsten filament, placed fifteen feet from 

 the aquarium, was found to make it more difficult to elicit 

 the phosphorescent response. When a number of individuals 

 were placed in the early morning in a dark-room, it was found 

 impossible six hours later to obtain light production in response 

 to mechanical stimulation unless the animals were strongly 

 pressed or struck. Induction shocks of moderate strength, how- 

 ever, did induce light production at any time, whether the 

 Ptychodera had been in darkness or in light. 



