24 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



changed to bring similar experiments together, while useless and 

 often repeated ones have been omitted, and short elliptical sentences 

 completed. Where the present writer wished to add any explanation, 

 the same has been placed in brackets. 



CHARYBDEA. 



Light and Darkness. 1. Eight medusae, in a deep glass jar and 

 covered by a black coat, except one inch around the top, were 

 placed in the dark-room. 



a. When light from a lamp was thrown on the surface (one 

 inch) layer, the animals were active near the surface ; when the 

 light was withdrawn, one or two were on the bottom and not moving 

 but were probably pulsating. 



b. After four or five minutes in the dark, three or four besides a 

 feeble one are on the bottom. It took about two minutes to get them 

 all to swim [by the lamp]. Of the three on the bottom, one, at any 

 rate, was not pulsating. [Three other attempts like a and b were 

 made, with very similar results.] 



2. Experiment No. 1 was repeated several weeks later. Four in 

 a large round glass dish were placed in the dark-room. A lamp 

 being held to the dish all but one were found to be on the bottom. 

 That one quickly went to the bottom, while two of those on the 

 bottom quickly came to the top. In two or three minutes the one 

 that had gone to the bottom began to pulsate and at about the 

 same time the other one that had remained on the bottom also 

 began to pulsate, while the two that had gone to the top stayed 

 there swimming very actively. [Repeated with like results.] 



3. Fresh ones did not show the reaction to light after darkness 

 so well as did those in the experiments previously recorded. They 

 were experimented with about nine A. M., while usually they were 

 tried later in the day. I had rather suspected from previous work 

 that they would not react so well when fresh. 



4. a. In walking with the jar (1) of jelly-fish of experiment 1 

 from the dark-room to the back porch of the laboratory (fifty steps), 

 in the bright sun and a cool breeze, all were found upon entering 

 the laboratory door to have settled to the bottom and most of them 

 to have ceased active swimming. In five minutes two or three were 

 swimming somewhat, and in five minutes more all but one or two 

 (eight in all) were swimming. 



