Morse, Behavior of Gonionemus. 455 



On Yerkes' explanation the direction of movement must ever 

 be directly away from the sun. In the present case it is obvious 

 that this would cause them to swim downward rather than into the 

 shadow. 



The trial and error method of response is nowhere better exem- 

 plified than in the reactions of the medusae to heat. The 

 observations of the writer will be briefly recounted. A glass 

 trough, 7.8 cm. in width, 26.8 cm. in length and 4 cm. deep, was 

 so placed that one end rested on a triangular copper bath while the 

 opposite end was surrounded by a freezing mixture. The extremes 

 were 36° C. and 2° C. Several medusae were put into the vessel, 

 where they began to swim in all directions. Four proceeded at 

 once to the heated end where they came to rest in a temperature of 

 about 35°. Four others swam to the opposite end and came to 

 rest in a temperature of about 5°. Obviously these were strong 

 swimmers and swam into a temperature which was too far beyond 

 their normal to recover. The great majority of the medusae were 

 to be found after a while in a temperature of from 20° to 30°. 

 Apparently this is an optimum. The medusae would be seen to 

 swim for some distance toward the heated end, turn, swim into 

 the cold end again, turn again and repeat the operation with the 

 general result that they finally settled in the zone of optimum 

 temperature. 



The writer is indebted to Dr. T. H. Morgan for suggesting the 

 work and for much kindly aid in the course of its preparation. 

 The writer wishes also so express his thanks to Dr. R. M. Yerkes 

 for much kindness shown him in this and other instances. The 

 work was done at the Woods Hole Station, U. S. Bureau of 

 Fisheries. 



The College of the City of New York, 

 September, 1906. 



LITERATURE LIST. 



Hargitt, C. W., '06. Experiments on the behavior of tubicolous annelids. Juurn. Exp. Zoo!., Vol. 3, 



pp. 295. 

 Jennings, H. S., '06. Behaviorof the lower organisms. Colun.h.a University, Biological Series, Vol. 10. 

 Mast, E. C, '03. Reactions to temperature changes in Spirillum, Hydra and fresh-water planarians. 



Amer. Jour. Physiol., Vol. 10, p. 165. 

 Perkins, H. F., '03. The development of Gonionema murbachii. Proc. Phila. Acad. Natr. Sc. for 



1902, pp. 750-790. 

 Romanes, G. J., '93. Jelly-fish, star-fish and sea-urchins. International Scientific Series. 1893. 



