ASSOCIATION AND COLOR DISCRIMINATION 453 



lying quietly in the bottom of the aquarium and are wary about 

 coming to the surface for food, the younger fishes swim about 

 actively, are less easily disturbed by jars and movements, and 

 take food more eagerly. But fry under one and a half inches 

 in length are undesirable for such work, as their movements are 

 irregular and unsteady. 



INSTINCTIVE MOVEMENTS 



Instinctive movements may be defined as locomotor responses 

 exhibited by an animal without previous training. Taken as 

 a whole, these responses make up what Jennings has defined as 

 the 'action' system, and they nearly always determine how any 

 animal is going to react under a given set of conditions. The 

 mudminnow and the stickleback have the same types of in- 

 stinctive movements, namely, swimming, leaping out of water, 

 and flopping about on land. The mudminnow swims rather 

 deliberately with a smooth motion. When accustomed to lab- 

 oratory conditions, it sometimes springs up and seizes objects 

 outside of the water. Before doing so, it usually hesitates a 

 short distance from the surface, switching its tail in an agitated 

 manner. If the tank containing the mudminnows is left un- 

 covered, the fishes are liable to leap entirely out of the recepta- 

 cle.^ Mudminnows bury themselves in the mud to tide over 

 dry seasons. 



The stickleback swims in a jerky, nervous manner, never going 

 far in one direction, but darting hither and thither. It leaps 

 out of water, but usually not so far as the mudminnow ; generally 

 it comes to the surface and bobs up and down, thrusting out 

 only its nose. It is less timid, though always wary. 



PERIODIC ACTIVITIES AND DAILY RHYTHM OF THE MUDMINNOW 



Seasonal variations in the activities of fishes are not readily 

 subject to laboratory observation. In almost all cases, however, 

 the best results in the training experiments to be described were 



' It is reported by Mast ('15) that Fundulus leaps from tide pools and succeeds 

 in transporting itself by flopping along on land across a barrier of dry ground 

 more than 3 m. wide and 10 cm. high. 



