276 C. M. CHILD. 



sure, since the force of the inward current through the oesoph- 

 agus is reduced. The force of circulatory currents in the body 

 must be similary reduced and consequently any local pressure 

 due to them is also reduced. 



Decrease in temperature is a condition which reduces ciliary 

 activity. It follows that in winter specimens the cilia must be 

 much less active than in summer specimens. Winter specimens 

 are visibly less distended than summer specimens. I can see no 

 escape from the conclusion that the atrophy of the tentacles in 

 winter specimens is due as in experimental pieces to a long-con- 

 tinued reduction to a relatively low level of the internal water- 

 pressure, resulting in this case from the reduction of ciliary 

 activity in consequence of low temperature. 



The fact that the shrivelling of the tentacle always begins at 

 the tip and proceeds gradually in the proximal direction is of 

 some importance. If this process is the result of decrease in the 

 general internal pressure why should the reduction proceed from 

 the tip? According to the laws of hydrostatics the internal 

 pressure must be the same in all parts of the enteric cavity, con- 

 sequently when reduction of the pressure occurs it occurs at all 

 points. This being the case why should a slight reduction of 

 pressure affect merely the tip of the tentacle, while a greater re- 

 duction causes atrophy of a larger part? 



In the present state of our knowledge two explanations of 

 this fact appear possible. It may be that the distal portions of 

 the tentacle exist under relatively unfavorable conditions of nutri- 

 tion as compared with the proximal portions. The small size 

 of the tentacular cavity in this region and the consequent im- 

 perfect circulation of fluid and also its distance from the central 

 cavity where most of the digestion probably occurs, afford a 

 possible basis for such an assumption. If the stimulus of internal 

 pressure is effective upon the tissues of Ceriantlius we should 

 expect to find the poorly nourished parts of the body more sen- 

 sitive than other portions to decrease in this stimulus. Accord- 

 ing to this view reduction of internal pressure might result in 

 atrophy beginning at the tips of the tentacles and proceeding 

 proximally according to the degree and duration of the re- 

 duction. 



