ORIENTATION IN COLONIAL ORGANISM 15 



tains favor this conclusion could be accounted for on the basis 

 of the change-of-intensity theory, even if the photo-sensitive tis- 

 sue were confined to a single median spot such that there could 

 be no balancing of effects on symmetrically located tissues. 



This author, moreover, comes to another conclusion that seems 

 to be supported by neither logic nor fact. He says (p. 271): 

 ''Bancroft's ('13) work, in which he showed not only that there 

 was a distinct reaction to constant intensity present in Euglena 

 but that it was largely the reaction to constant intensity which 

 determined its orientation, shows the untenability of Mast's 

 sweeping statement in one of the forms on which Mast himself 

 worked." What is this sweeping statement? Our author 

 quotes it as follows (p. 270) : 



Mast ('11, p. 234) says: There is no conclusive evidence, except per- 

 haps in animals with image forming eyes, showing that light acts con- 

 tinuously as a directive stimulus, that symmetrically located sides are 

 continuously stimulated .... (p. 235). Light no doubt acts 

 on organisms without a change of intensity much as constant tempera- 

 ture does, making them more or less active and inducing changes in the 

 sense of orientation; but there is no conclusive evidence showing that 

 light acting thus ever functions in the process of orientation. 



Is it not perfectly obvious that the results of Bancroft's in- 

 vestigations presented in 1913, assuming that they are as quoted 

 above, do not have the slightest bearing on the validity of this 

 statement, made in 1911? Does the discovery of a certain re- 

 sponse at a given time make untenable the statement that it 

 had not previously been discovered? 



Whatever the final conclusion may be regarding the two theo- 

 ries of orientation in question the fact that many reactions in 

 animate systems depend upon the time-rate-of-change of stimu- 

 lating energy is well established. These reactions are of great 

 interest, partly because they are exceedingly rare in inanimate 

 systems, and a thorough study of them cannot fail to yield in- 

 teresting results. 



