100 G. H. PARKER 



expressed in this paper that an increase of internal pressure be- 

 yond a certain point will call forth a vigorous muscular contrac- 

 tion. If, however, this mild pressure is not exceeded, a tentacle 

 expanded to about two-thirds its natural length and exhibition 

 its normal pliability is readily obtained. 



The response of the tentacles to internal pressure is probably 

 not without its significance in the general reactions of actinians. 

 When a sea-anemone contracts vigorously, its fluid contents are 

 put under much increase of pressure and this increase must be 

 almost instantly transmitted to the contents of each tentacle, 

 thus stimulating it to contraction. In this way the whole circle 

 of tentacles might easily be brought to general withdrawal 

 through the individual response of the neuromuscular mecha- 

 nism of each tentacle acted upon by a common purely physical, 

 factor. The ease with which such a controlling factor could be 

 confused with nervous influence must be apparent. 



Having obtained in isolated tentacles a close approximation to 

 the resting condition of the attached tentacles, it remained to 

 compare the reactions of these two classes. Suspended tenta- 

 cles filled to about two-thirds their natural length will remain 

 quiescent in sea-water for a considerable period. From time to 

 time, however, they show spontaneous movements consisting of 

 slight contractions and twistings by which more or less of their 

 contained fluid will be discharged. If this is replaced they will 

 reexpand and thus periods of quiescence are followed by periods 

 of spontaneous movements. In these respects the severed ten- 

 tacles reproduce very closely the behavior of the normally at- 

 tached tentacles. 



If a suspended tentacle is gently touched it exhibits irregular 

 reaching and writhing movements, whereby it will partly empty 

 itself. After it has been refilled, a more vigorous stimulus will 

 induce a more or less spiral contraction, in which state the ten- 

 tacle will remain some minutes. Again it must be refilled. In 

 the response both to the slight and to the vigorous mechanical 

 stimulus the severed tentacle reproduces in a most striking way 

 the movements of the attached tentacles under like stimulation. 



