362 



University of California Piihlications. 



[Zoology 



dependent on the length of the are of the circle completed by the 

 anterior end. Unfortunately these movements were not observed 

 when India ink or carmine was in the water. While it would 

 seem natural to suppose that the cilia at such times must beat 

 transversely to raise the body, it can be said that in the other 

 movements no case of the transverse stroke was noted, even under 

 the most favorable circumstances. 



13. 14. 



Fig. 13. — Occasional movements during gliding ^\hic'h probably call in the 



transverse action of the cilia. 

 Fig. 14. — Entarv movoments during gliding wliieli jirobably call in the 



transverse action of the cilia. 



The membi'anellae play a considerable part in the motor re- 

 action. The anterior edge of the adoral zone and the left lip of 

 the buccal groove are lined by these organs. The normal beat of 

 the memln-anellae is from right to left. At the moment of stimu- 

 lation all the membranellae reverse their action ; then those of 

 the buccal groove resume their normal stroke beating slowly 

 backward, and those of the anterior end also resume their normal 

 beat from right to left. During the remainder of the action all 

 the membranellae continue their normal beat. The membra- 

 nellae of the buccal groove under strong stinuilus may continue 

 reversed for some time, but those of the anterior end never con- 

 tinue beyond the moment of contact, after which they resume 

 their beat towards the left with increased vigor. This action 

 tends to throw the anterior end to the right and thus aids in the 

 execution of the motor reaction. The action resulting from the 

 membranellae is illustrated by fig. 15. A large animal was 



