SOME LIGHT REACTIONS OF THE MEDUSA 



GONIONEMUS. 



L. MURBA.CH. 



In the following notes it is my purpose to record some obser- 

 vations I have made on the behavior of Gonionemus ' to light, 

 after the experiments made a few summers ago on the reactions 

 of its subumbral papillae to light, and to include in the discus- 

 sion points on which other observers are not agreed. I shall 

 refer only to these publications. 



After observing the behavior of Gonionennts for a considerable 

 time the following brief statements will be found to hold con- 

 cerning their habits. As darkness approaches the medusae be- 

 come restless in their native haunts where they are either lying 

 inverted on the bottom, the apex of the bell being heavier, or 

 clinging to plants and other submerged objects. Although all 

 the tentacles in this species have adhesive pads near the free end, 

 yet the animals attach by only a few, the remaining tentacles 

 being spread out in all directions ready to catch their passing 

 prey. When still daylight above the water it is becoming dusk, 

 we may say, at their depth, and among the plants from one half 

 to several meters deep. Within an hour after dark the eggs and 

 sperm are deposited and their intermingling in the sea water in- 

 creases many times their chance of development. Thus their 

 locomotion in early evening is of great value as then more eggs 

 will be fertilized. The dehiscence of the eggs and sperm has 

 been shown to be due to the diminution or withdrawal of light, 

 and seems rather direct evidence of an external stimulus causing 

 a physiological change. For considerable time after the dehis- 



1 There would seem to be no need of stating that the Woods Hole species is the 

 one under consideration. The experiments on which these notes are based were made 

 at the Marine Biological Laboratory, at intervals between other work in the summer. 

 I gladly acknowledge the courtesy of the Director in continuing to grant the neces- 

 sary facilities. It will be found that some points differ from a report made on this 

 subject in the winter before the Michigan Academy of Science (Annual Report, 

 1909) as I have been able to make additional experiments this season. 



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