Phosphorescence in Ctenophores. 107 



in motion and yet without being accompanied by phosphorescence. 

 When in a dark period phosphorescence was seen, the hght was 

 immediately turned on, and it was observed that the ctenophore 

 was adjacent to the side of the dish and had probably struck it in 

 the course of locomotion. A slight mechanical stimulus, such as 

 touching the animal with a glass rod, jarring the dish, or the table 

 upon which it was placed, easily elicited the response of phos- 

 phorescence, both before and after the experiment described 

 above. It was clear that the animal was capable of phosphores- 

 cence during all the periods of locomotion, but the necessary 1 

 mechanical stimulus was absent except when the ctenophore came 

 into contact with the side of the dish. ' 



2. hi Embryos. 



Further observations were directed toward finding how far 

 back in the ontogeny of the animal phosphorescence could be 

 traced. The eggs were obtained as follows: On August 6, some 

 ctenophores were brought into the laboratory and placed in glass 

 evaporating dishes each containing about two liters of the sea- 

 water brought in with them. Two animals were placed in each 

 dish. The water was changed once or twice, only such being 

 used as was brought directly from the sea. On the morning 

 of August 7, a layer of eggs in various stages of development was 

 found upon the bottom of each dish. By withdrawing the sea- 

 water above them and replacing it with fresh sea-water about 

 twice a day, they were reared to fully formed young ctenophores. 

 In no instance were eggs observed to be deposited in the day time. 



When a lot of eggs had developed to the stage in which the four ! 

 sets of paddle plates first appear, phosphorescence could be 

 demonstrated. If at night the embryos were stirred with a glass 

 rod, or the dish containing them was jarred, numerous phos- 

 phorescent specks would appear momentarily. The experiment 

 did not easily succeed in the day time, even if the eggs were kept 

 in the dark-room. Perhaps the same rhythm in the intensity of 

 phosphorescence belongs to them as to the adults. In the latter \ 

 it was observed (1903) that phosphorescence was more intense 

 and more easily excited at night than during the daytime, even [ 

 when the animals were kept continuously in the dark-room. 

 Furthermore, the phosphorescence of these embryos could not be 

 indefinitely repeated, but was exhausted after a few flashes. In 



