6 L. MURBACH. 



from one or two to three days after the tissues in question were 

 removed. 



Results. 



In all cases where papillae were removed reactions still con- 

 tinued. As soon as such animals as had also the nettle welt 

 removed were tested, the experiments were seen to be confirma- 

 tory of those on the papillae. There was always a definite response 

 to light stimulus, but in some cases it was slow. And it is still 

 noticeable that the oral side of the medusa was more sensitive to 

 light than the aboral. It ought to be stated here that the velum 

 was always removed with the welt of tissue and it was not neces- 

 sary to wait for its regeneration in order to get responses to light. 



To determine if any of the other marginal organs or even any 

 of the organs on the oral side of the animal had anything to do 

 with the light perception, exclusively, or whether, as I began to 

 think, it was the function of more than one organ — perhaps the 

 subumbrellar epithelium in general — other organs which it was 

 thought might be stimulated by light were removed. The ovaries, 

 the velum, and the tentacles were in turn cut away. It is diffi- 

 cult to remove the velum entirely, as the closest cutting that can 

 be done with the finest scissors leaves a narrow bit of the attach- 

 ment of the velum on the margin. However, since the velum 

 may be entirely removed while removing the welt and papillae, 

 a differential result will give approximately the value of the 

 velum. Although these operations are more or less severe for 

 the size of the organism, yet I have never observed so severe a 

 shock from any of them as recorded by Yerkes, viz., that they 

 have not again recovered. Indeed, I have almost always removed 

 all the tentacles together and do not remember to have lost any 

 individuals from this cause. 



A preliminary experiment on a normal one, one without ovaries, 

 one without tentacles, one without the welt and papillae, resulted 

 as follows ; For the normal the average reaction time was y^ 

 seconds ; for the one without ovaries io| seconds ; for the one 

 without tentacles 2o|- seconds ; for the one without nettle welt 

 and papillae 1 2-| seconds. In the light of later observations these 

 results, except the last, seemed too long, as those without ten- 



