312 EDWARD C. DAY 



sequence occurred by stimulating the other half first. Thus the 

 wave of stimulation could travel in either direction around the 

 cut. No effort was made to determine whether this stimu- 

 lation wave was of the nature of a nerve impulse, or whether it was 

 simply a wave of muscular contraction which depends for its 

 completion upon the continuity of the muscle tissues ; nor further, 

 whether the length of the latent period was dependent upon the 

 intensity of the stimulus to any degree, or in how far it was 

 affected by the depth of the incision. 



B. Amputation of siphons 



When an Ascidia mentula was narcotized with cocain, the 

 oral siphon amputated below the circlet of oral tentacles, and 

 both the animal and the amputated piece were put into fresh 

 sea-water ^nd allowed to recover, the aboral siphon showed a 

 return of sensitivity in a little over an hour while the amputated 

 siphon did not regain sensitivity until two or three days after 

 the operation. When the operation was performed without first 

 narcotizing, recovery of the amputated piece took place in 

 twelve to fourteen hours, whether it was the oral or aboral 

 siphon. 



Similar operations on the siphons of Ciona intestinalis revealed 

 a greater recuperative power than that of Ascidia mentula, 

 amputated siphons recovering sensitivity twenty-five minutes 

 after the operation. 



The siphons possess, therefore, an irritability which is inde- 

 pendent of any connection with the nerve ganglion. The thresh- 

 old of stimulation lies higher for amputated siphons than for 

 the intact siphons, it requiring a stronger stimulation to elicit 

 a response. This diminution in sensitivity was probably oc- 

 casioned in part by the insufficient blood supply due to the 

 operation, with a consequent lack of oxygen and an accumulation 

 of catabolic products, and in part by the interruption of the 

 nerve reflex. The presence or absence of the rings of oral 

 tentacles made no obvious difference in the general responsive- 

 ness of the amputated oral siphon. 



