AMEBA 53 



of food, were allowed to desiccate, and were transferred to water 

 from different localities; none of these resulted in encystment and 

 sporulation. 



The development of Ameba is simply a matter of growth; 

 both the spores and the daughter cells resulting from binary divi- 

 sion become full-grown specimens by means of a gradual increase 

 in volume. 



Behavior of Ameba. The sum total of all the various move- 

 ments of an animal constitute what is known as its behavior. 

 In Ameba these movements may be separated into those con- 

 nected with locomotion and those resulting from external stimuli. 

 We have already given an account of the locomotion of Ameba, 

 and so shall confine ourselves now to a discussion of its responses 

 to different kinds of stimuli. The reactions of Ameba to stimuli 

 have been grouped by Jennings (39, 41) into positive, negative, 

 and food- taking. The last named were discussed on page 47. 

 The following account, then, will deal with positive and negative 

 reactions of Ameba proteus to external stimulation. 



Definitions of Terms. First, it will be well to define a few of 

 the terms used in describing the motor responses of animals to 

 stimuli. A reaction resulting from a change in an animal's 

 environment, e.g. an increase in the intensity of the light, is 

 known as " tropism " or " taxis." The term " tropism " means 

 " to turn "; it is used instead of saying that an animal " likes " 

 or " dislikes " certain stimuli, because we can determine by ex- 

 periment which way an individual will turn under various condi- 

 tions, but are not in a position to decide whether " likes " or 

 " dislikes " enter into the phenomena. The kind of stimulus 

 employed is indicated by a prefix. The principal kinds of tro- 

 pisms are as follows: 



(1) Thigmotropism = reaction to contact. 



(2) Chemo tropism = reaction to a chemical. 



(3) Thermotropism = reaction to heat. 



(4) Phototropism = reaction to light. 



(5) Electrotropism = reaction to electric current 



