Behaviour of Hydroids 65 



means that the prompting cause of purposive 

 action is energy derived from external or 

 internal sources acting through sensory organs, 

 which, by practice have become sufficient to 

 provide for the necessities of the classes 

 of animals we have referred to in their 

 struggle for existence, and for their repro- 

 duction. 



Professor Preyer informs us that on slipping 

 a piece of rubber tubing over the middle part 

 of one of the arms of a star-fish, belonging to 

 a species in which those members are very 

 slender, he found that the animal tried succes- 

 sively various devices to get rid of the foreign 

 body; by rubbing it against the ground, trying 

 to shake it off; holding the tube against the 

 ground with a neighbouring arm, and finally, 

 as a last resort casting off the limb together 

 with its rubber ring. 1 Action of this kind is 

 probably due to the overflow of nervous energy 

 set free by the stimulus excited by the pressure 

 of the rubber tubing on the sensory organs of 

 the limb. Most people, however, refer these 

 movements to "spontaneous action," which is, 



1 The Animal Mind, by Margaret F Washburn, p. 215. 



E 



