266 University of California Publications in Zoology [Vol. 11 



TABLE VI 



Acclimatization to Shadows as Expressed in Number of Seconds 



Cessation of Undulatory Movements in Five 



Specimens of Dina microstoma 



This supposition is supported by the fact that the central ap- 

 paratus is much more susceptible to the effects of fatigue than 

 the afferent or efferent nerves. It is not a fatal objection to the 

 theory of fatigue that the response falls off very quickly. An 

 extreme sensitiveness may result from a certain condition of 

 balance which a slight chemical change might overthrow without 

 rendering the organism insensitive to stronger stimuli. ' ' 



That in the acclimatization experiments conducted on Dina 

 microstoma the changed responsiveness of the organism is not 

 due to a fatigue of the muscular motor apparatus is well borne 

 out by the fact that after the animal has failed to respond to 

 several previous light stimuli a stronger jar will produce a cessa- 

 tion of the undulator.y movements. The phenomenon is very 

 different from that involved in the death feint, where the entire 

 state of the organism appears to be changed, as is the case in 



