1914] Sharp: Diplodinium ecaudatum 99 



membranelles resemble those of the dorsal zone. Normally the wave 

 of contraction starts at the junction of the heavier adoral membra- 

 nelles with the finer oral cilia and passes first to the right and then 

 ventrally and to the left, to end at the left extremity of the adoral 

 row of membranelles. The movement of the individual adoral mem- 

 branelle is the same as in the case of the dorsal membranelles, i.e., 

 circumduction. 



A second interesting observation was to the effect that any single 

 membranelle or any set of membranelles of either zone could be moved 

 at the point of stimulation, by simple contact, or even independently 

 of any apparent stimulus, and this without disturbing the other mem- 

 branelles, either of the same zone or of the other zone, a phenomenon 

 which reminds the observer of the result obtained by stimulating a 

 single tentacle or set of tentacles of the sea anemone. This fact leads 

 to the belief that each penicillate membranelle is supplied by an 

 individual "nerve fiber." As the oral cilia have never been observed 

 in a quiescent state, it is impossible to be certain of the direction of 

 their wave contractions. 



When the temperature drops too low or the animal is otherwise 

 irritated, either mechanically or chemically, the oral region, viz., 

 the oral cilia, the oral disk, and the oral opening, is retracted pos- 

 teriorly into the body. Simultaneously with this the inner adoral and 

 inner dorsal lips are extended in such a manner as to become directly 

 continuous with the outer adoral and outer dorsal lips respectively, 

 that is to say, the outer furrows are obliterated and the two lips are 

 smoothly continuous one with the other. When the oral region is sud- 

 denly retracted the popping out of these inner lips reminds one of 

 the popping out of the inverted finger tips of the surgeon's rubber 

 glove when everted by air pressure. And a similar explanation is 

 applicable to both. In other words, the protrusion of the inner lips 

 is a mechanical occurrence brought about through the contraction of 

 the oesophageal fibers, which pulls the oral region into the anterior 

 end of the body and thus increases the pressure in the semifluid 

 ectoplasm. According to the laws of physics, pressure is transmitted 

 equally in all directions. Hence when the increased pressure due to 

 the inward pull of the oesophageal retractor strands is sufficient to 

 overcome the resistance offered by the weakest portion of the contain- 

 ing wall that weakest portion will yield sufficiently to bring again 

 the pressure relations to an equilibrium. In this case the weakest 

 portions of the retaining wall are the inner adoral and the inner dorsal 



