14 S. O. MAST 



conclusions regarding the orientation of Eudendrium which are 

 in harmony with the work just mentioned, and Loeb and Ewald 

 ('14) support these conclusions. Ewald ('14) also maintains 

 that certain responses in Daphnia are proportional to the amount 

 of stimulating energy; at any rate that they are not dependent 

 upon the time-rate-of-change of such energy. Patten ('14) comes 

 to the same conclusion regarding orientation in blow-fly larvae. 

 He says (p. 272) : ''Orientation in the blow-fly larva depends to 

 a large extent on the stimulating effect of constant intensity. 

 The reaction to light of constant intensity follows the Bunsen- 

 Roscoe law." 



Both Ewald and Patten base their conclusions upon the fact 

 that the reactions observed at the intersection of two beams of 

 light were the same when the light in one beam was intermittent, 

 as they were when it was constant in both, provided the relative 

 amount of energy in the two beams was the same under both 

 conditions, and provided that the intermission was relatively fre- 

 quent and con^tinuous. 



It seems to me that these results do not show that the reac- 

 tions referred to in Daphnia and the process of orientation in the 

 blow-fly larvae are necessarily dependent upon the continuous 

 action of the light as maintained by Ewald and Patten, All that 

 they actually demonstrate is that if the intermission is of suf- 

 ficient frequency, periodic illumination acts the same as continu- 

 ous illumination. This is true for the human eye and yet no 

 one holds that this in itself precludes the possibility that stimu- 

 lation is dependent upon time-rate of change of energy. More- 

 over, Patten in his work on the fly larvae did not eliminate 

 changes of intensity on the sensitive tissues in the larvae due to 

 the alternate extension and retraction of the anterior end, con- 

 sequently the reactions observed in the process of orientation in 

 these animals may have been due to these changes without ref- 

 erence to the amount of light energy received. 



Patten's conclusion (p. 272) that ''orientation to light from 

 two sources depends on the relative amount of stimulation re-* 

 ceived by symmetrically located sensitive areas" is equally pre- 

 carious. As a matter of fact, all of the responses which he main- 



