MOVEMENTS OF TENTACLES IN ACTINIANS 103 



an immediate shortening. These tests were repeated several 

 times and always with the same outcome; a shortening after 

 two or three seconds when the stimulus was applied to the in- 

 terior of the tentacle and a sudden shortening when it was ap- 

 plied to the exterior. When mussel juice was substituted for 

 acetic acid, a writhing response was produced in about four sec- 

 onds by the application of this stimulus to the inside of the ten- 

 tacles, but this response took place almost immediately when the 

 juice was applied externally. Quinine hydrochloride in one per 

 cent solution was immediately effective when applied to the ex- 

 terior and called forth a response only after more than a minute, 

 when applied internally. 



It thus appears that stimuli which call forth specific reaction 

 when applied to the ectoderm of the tentacles induce the same 

 movements when they are applied to the entoderm, but only 

 after a somewhat longer interval. 



Is this difference in the rate of response a difference in the 

 nervous activities of the ectoderm and the entoderm of the ten- 

 tacle or is it to be accounted for by the direct stimulation of the 

 ectoderm in the quick form of response and the less direct one 

 in the slow form in that in the latter it requires an appreciable 

 time for the stimulating fluids to pass from the cavity of the 

 tentacle through its wall to the ectoderm? If the latter expla- 

 nation is correct, it ought to be possible to get evidence of the 

 penetration of the wall of the tentacle by such a solution as that 

 of acetic acid. 



To test this question an isolated tentacle was suspended in 

 seawater and close to it was hung a piece of blue litmus paper; 

 near at hand in the seawater was also suspended a piece of red 

 litmus paper. Deep into the seawater filling the tentacle was now 

 discharged about a drop of one per cent acetic acid. The ten- 

 tacle contracted slightly but not enough to cause it to overflow. 

 In about half a minute the blue piece of litmus paper began to 

 redden, showing that the acid had transfused the living walls of 

 the tentacle. Meanwhile the piece of red litmus paper had be- 

 gun gradually to change blue, doubtless from the slight alka- 

 linity of the seawater. In two other tests evidence of the pene- 



