102 G. H. PARKER 



lated tentacles are not exact duplicates of those of the attached 

 ones. They are feebler and less precise, but aside from these 

 peculiarities they are so strikingly similar that their resemblance 

 is the conspicuous feature of the operation. The differences be- 

 tween the two sets of reactions are due in my opinion to the 

 partial contraction of the excised tentacles. This partial con- 

 traction, as already pointed out, seems to be purely operative in 

 its source, and it is this, in my opinion, that is the cause of the 

 lowered responsiveness rather than the absence of some extra- 

 tentacular influence. That this explanation is correct, may be 

 shown by stimulating unsevered tentacles that are already in a 

 state of partial contraction due to a preceding stimulation. When 

 such a tentacle is restimulated, it responds, as repeated trials have 

 shown me, with just that partial vigor and lack of precision which 

 characterize the isolated tentacles. I, therefore, believe that we 

 have ample grounds for concluding that the slight differences in 

 the reactions of isolated and attached tentacles are purely 

 operative. 



The tentacles of Condylactis, like those of most actinians, pos- 

 sess a longitudinal musculature in the ectoderm and a circular 

 one in the entoderm and are supposed to exhibit a nervous layer 

 with each muscular layer. The means of stimulation thus far 

 used in these experiments have been applied to the ectoderm and 

 the responses thus called forth have been chiefly in the longi- 

 tudinal muscle of this layer, though the deeper circular muscle 

 has undoubtedly also been generally involved. With tentacles of 

 the size of those in Condylactis it is possible to apply stimuli to 

 the entodermic surface as well as to the ectoderm and by this 

 procedure some idea of the responsiveness of this surface can be 

 obtained. 



Into an isolated tentacle suspended in seawater by a hook 

 and so held that its open end was well above the surface of the 

 water, a small amount of one per cent acetic acid was injected. 

 After about two seconds the tentacle gradually shortened. It 

 was then thoroughly washed with seawater and rehung. When it 

 had become reexpanded, the discharge of a small amount of one 

 per cent acetic acid on the ectodermic surface was followed by 



