HABITS AND REACTIONS OF LACRYMARIA 239 



the body is lodged in debris or rests against some object that 

 the anterior end is fully extended. It would thus seem that 

 the body must be held in order that full extension of the neck 

 may occur. While the neck stretches out under such conditions, 

 it can often be seen that the body moves slightly forward as 

 though it were straining the tangle which holds it, but as soon 

 as the head stops or returns the body settles back to its original 

 position again. I have repeatedly seen this when the cilia on 

 the body were at rest. The forward movement must therefore 

 have been due to a pull on the body from the anterior end. 

 If the head were thrust out in place of pulled out, the body, 

 provided the cilia on it be inactive, would move backward, 

 while the head advances, in place of forward as was actually 

 observed. 



(3) The oral cilia are always active while the head is moving 

 forward and quiet while it is moving backward. Many observa- 

 tions were made with reference to this and in e\-ery case it was 

 found that the oral cilia become active simultaneouslv with the 

 beginning of forward movement of the head and strike backward, 

 but that as soon as the head starts to return they strike forward 

 a few times and then fold in over the oral knob and remain 

 quiet. When the head turns toward one side the cilia on the side 

 toward which it turns strike forward and those on the opposite 

 side strike backward. This was distinctly seen several times in 

 detached heads. These observations show that the forward and 

 lateral movements of the head may be due entirely to the activity 

 of the oral cilia and that the backward movement is probably 

 due to the contraction of the neck. 



It is thus evident that the behavior of this animal is dom- 

 inated to a very large extent by the activity of the oral cilia. 

 Not only is the direction of locomotion of the entire animal 

 regulated by them and the extension and the lateral movements 

 controlled by their reactions, but they may also furnish much of 

 the motive force in swimming. One often sees individuals 

 swimming about with the body curved so as to form a hook 

 which extends almost at right angles to the direction of loco- 

 motion, showing clearly that the body cilia are temporarily 

 at least practically inactive and that the oral cilia alone are 

 functional in producing forward movement, that the body is 

 being pulled through the water by the action of these cilia, 



