238 S. O. MAST 



In teasing with needles the debris in which Lacrymaria are 

 found, one occasionally tears off the anterior end of specimens 

 and thus accidentally performs an operation which would other- 

 wise be exceedingly difficult owing to the small size of the 

 creatures and their constant motion. The movernent of four 

 pieces thus torn off" were studied in detail. One of these pieces 

 consisted of the head and a portion of the neck about as long as 

 the body, another was torn off immediately back of the band of 

 oral cilia and the other two were between these in length. They 

 lived and were active from three to five minutes. The reactions 

 in all were essentially the same. They swam about rapidly, 

 stopped, turned freely and sharply in any direction; in short, 

 the movements and responses of these detached segments were 

 strikingly similar to those of the head while still attached to 

 the body. The only essential difference to be seen is that after 

 stimulation there is very little if any backward movement of 

 the detached heads, whereas, in the attached heads under like 

 conditions, it will be remembered, there is marked backward 

 movement. This indicates that the extension and the lateral 

 movements of the anterior end in Lacrymaria are regulated 

 principally by the activities of the oral cilia, that this end is 

 not thrust out, but pulled out, not swung from side to side by 

 unequal tension of symmetrically situated tissues in the neck, 

 but pushed from side to side by the action of the cilia ; and that 

 the principal function of the elastic tissue in the neck is to draw 

 the. head back by contraction. These ideas are further supported 

 by the following observations: 



(i) In specimens with the head cut off immediately back of the 

 oral cilia the neck is extended only a little and moves but slightly 

 from side to side, although they swim about freely, forward and 

 backward much like normal specimens. In fission the oral cilia of 

 the posterior individual do not develop until some time after 

 separation takes place. Thus we have two individuals, the 

 anterior with oral cilia, the posterior without; and we find that 

 while the neck of the former stretches out normally, that of the 

 latter extends relatively but little. This indicates that while 

 the neck can be thrust out somewhat by the action of internal 

 tissue, the oral cilia are necessary for full extension. 



(2) When Lacrymaria is free the neck rarely projects to a 

 distance equal to twice the length of the body. It is only when 



