LIGHT RECEPTIVE FUNCTION OF GONIONEMUS. 5 



be remarked here that in the latter case the reactions were 

 generally slower. The exposure was made in sunlight varying 

 as it does during the middle portion of the day. For shutting 

 out the sun absolutely opaque material was used ; in some cases 

 plain covers, in others covers that would completely darken the 

 dish. While these give varying results in reaction time, they 

 will not be considered here since constant conditions were main- 

 tained throughout any one experiment. In accurate time reac- 

 tion experiments there should be some means of determining the 

 exact intensity of light used. In some cases the exposure was 

 uniformly for 60 seconds ; in the earlier experiments only until 

 reaction took place. The rest period I varied from 30 to 300 

 seconds ; in general I found the former too short and the latter 

 too long. Contraction leading to displacement was counted a 

 reaction. From five to ten observations were made in succession 

 and tabulated, but space will not here be taken for the tables in 

 full. Only about one half the averages obtained will be given. 

 It will be seen that I have followed somewhat generally the 

 methods of Romanes, 1 Conant and Berger, 2 and Yerkes. 3 



Having received response to light in all cases where the mar- 

 ginal papillae had been carefully removed, another cause of the 

 reaction was looked for. Now as there is a thin welt of tissue 

 connecting the papillae which appears to be made up of similar 

 cells, having about the same color, this welt of tissue might be 

 conceived as taking over any light-percipient function that the 

 removed papillae were thought to possess ; it was accordingly 

 also removed. As this is a much more painstaking operation 

 the work necessarily progressed slowly. In some cases a method 

 was employed somewhat similar to the one previously adopted in 

 removing the otocyst organs in the same medusa. 4 In other 

 cases I depended on cutting away as little of the margin as pos- 

 sible and yet removing the welt of tissue in question, together 

 with the papillae. Such operated medusae were usually tried in 



1 Romanes, G. J. ('76), "Jelly-fish, Star-fish and Sea-urchin," International 

 Sc. Series, 1885. 



2 Berger, E. W., Mem. Biol. Lab. Johns Hop. Univ., Vol. IV., 4. 



3 Loc. cit. 



i Murbach, L. ('03), "The Static Function in Gonio7iemus," Am. Jour. Physiol., 

 Vol. X., No. 4, December, 1903. 



