Vol. 3 J 



Bovard. — Condylostoma patens. 



363 



swimming downwards in an aquarium, and when the anterior 

 ^end came in contact with the bottom, it spun around to the right 

 without backing up while the posterior end was still elevated. 



Attention is called to fig. 16 of a large individual swimming 

 down towards the bottom of an aquarium clouded with India 

 ink. As the animal struck the bottom it gave the motor reaction, 



Fig. 15. — The action of the membranellae causes the animal to swing to the 

 right. 



Fig. 16. — Tlie particles of carbon thrown to the left by the action of the 

 membranellae. 



all body cilia reversed, and the membranellae increased their 

 activity as shown by the force with which the carbon particles 

 were thrown to one side. There was no transverse action of the 

 body cilia in this case. During the backward movement and the 

 pause just before moving forward again, the increased activity 

 of the membranellae would have much to do with the turning of 

 the animal toAvard the right. 



To sum up. at the moment of stimulation the membranellae 

 reverse and then resume again their normal beat, with the ex- 

 ceptiou that those of the anterior end are more active. The 

 cilia all reverse, producing a backward movement of the animal. 

 Under a weak stimulus those of the left side may be reversed but 

 a short time and resume their normal beat. The myonemes on 

 the left side contract and produce a sharp curvature in the pos- 

 terior end of the body which causes the animal to turn towards 



