40 



ANIMAL AGGREGATIONS 



current. Jennings (1906), in his discussion of this reaction, says, 

 ''When a Paramecium is transverse or obUque to the direction of a 



1 2 



Fig. I. — (i) Arenicola larva in the free-swimming state proceeding on a spiral 

 course, m, n, Directions of light; a-/i, positions in the spiral. Larvae react to changes 

 in ray direction in positions b or d, but not in positions a and e. (2) Much enlarged 

 sketch of larval head. The eye-spots are composed of a dark-brownish part y and a 

 clear part x. Note the ciliary bands on (2) which are a part of the locomotor system. 

 (From Mast, Liglit and the Behavior of Organisms; courtesy of Wiley & Sons.) 



current at the time when the circuit is closed (Figure 2) certain strik- 

 ing effects are produced. If a current of medium strength is em- 



