240 S. O. MAST 



for any effective action of the body cilia would, under the con- 

 ditions mentioned, produce much greater sidewise movement 

 than is observed. 



Thus it may be assumed that the head of Lacrymaria behaves 

 much like an independent organism attached to the body by 

 means of highly elastic tissue, far more elastic than rubber of 

 the best quality, for that can be stretched only eight to ten 

 times its own length, while the neck of this creature can be ex- 

 tended approximately fifty times its length when contracted. 



What has been said above regarding the explanation of the 

 behavior of the entire organism applies also to the movements 

 of the head, but there is one phenomenon observed in the latter 

 that I wish to consider more in detail here. 



It will be remembered that when the head of Lacrymaria 

 turns toward a given side the oral cilia on .that side strike forward 

 while those on the opposite side strike backward. This difference 

 in the action of these cilia is independent of the character and 

 the location of the stimulus. As a matter of fact it occurs with- 

 out any apparent external change whatever. It is therefore 

 evident that the direction of turning in this animal must be 

 determined by internal conditions. And this is true with refer- 

 ence to many other lower organisms. Some of these organisms, 

 e. g., Paramecium and Oxytricha, are clearly asymmetrical and 

 in these the direction of turning is associated with their struc- 

 tural asymmetry. Others, however, e. g., CEdogonium swarm- 

 spores and Didinium, are like Lacrymaria, radially symmet- 

 rical. In these we find cilia somewhat similar to the oral cilia 

 in Lacrymaria and in the process of turning the cilia of the 

 former act just like those of the latter. But CEdogonium and 

 Didinum like Paramecium and Oxytricha always turn toward 

 the same side, and whenever they turn the same cilia strike 

 forward, while those on the opposite side strike backward. To 

 account for this it is only necessary to assume a fixed internal 

 structural or physiological differentiation. 



Lacrymaria on the other hand can turn toward any side. The 

 same cilia are consequently not always involved in the forward 

 stroke in the process of turning as is true for Didinium and 

 CEdogonium. In this creature the oral cilia on any side may 

 strike forward while those on the opposite side strike backward. 

 To account for the change in the action of the different oral 



