LIGHT RECEPTIVE FUNCTION OF GONIONEMUS. 7 



tacles or gonads displayed a remarkable activity, probably due to 

 the removal of these organs. 



In one of the first experiments a normal medusa was compared 

 with two of the same lot in which the marginal nettle welt and 

 papillae were removed. The averages of ten trials were as fol- 

 lows : Average reaction time of the normal medusa 8-| seconds ; 

 a 12 mm. olive-colored operated medusa 9^ seconds; a 6 mm. 

 yellow orange operated medusa 1 2 seconds. Next to this in reac- 

 tion time were the medusas with gonads removed. The average 

 of four sets of experiments was 1 3^ seconds. For the velum the 

 average was higher, being 27$- seconds ; and for the tentacles still 

 higher being 29 seconds. Another case, four hours after removal 

 of the tentacles gave an average of four seconds. 



Discussion. 

 Now, comparing these, account must be taken of the opera- 

 tions necessary for the experiments. The removal of the tentacles 

 is the simplest of all and least likely to prejudice the action of 

 other parts, therefore these results are the least doubtful. The 

 careful removal of the gonads can have very little detrimental 

 effect, as no principal part of the nervous system is involved. 

 The removal of the marginal papillae may include some of the 

 underlying tissues, and more of this is included when the nettle 

 welt is removed in addition. The same is true when the velum 

 is completely removed. In the experiment for the value of the 

 velum the attaching margin had to be left in order not to injure 

 the nerve ring too seriously. In view of these facts negative 

 results after any similar operation, such as Yerkes obtained for 

 the removed papillae, must be looked upon as needing confirma- 

 tion in other ways, rather than being considered a proof of the 

 function ascribed to the organs under consideration. In the 

 specimens without the attachment of the velum, and those with 

 the nettle welt and papillae removed we must bear in mind that 

 parts of the nervous system are more or less affected. 



Conclusions. 

 From the earlier experiments of removing the papillae alone it 

 is evident that they are not exclusively the organs of light stim- 



