2/8 C. M. CHILD. 



rolled portion. In all cases of this kind tentacle-regeneration is 

 much delayed and never proceeds far. 



2. It is possible by reduction of the internal water-pressure to 

 cause reduction of fully grown normal tentacles in both C. soli- 

 tarins and C. inembranaceus. The first stage in the reduction 

 consists in a gradual decrease in length and size of the tentacles : 

 in C. inembranaccns no further change was observed, but in C. 

 solitarius shrivelling and atrophy of the tentacles began at the 

 tips if the reduced pressure continued. In specimens which were 

 kept widely open the tentacles were reduced to mere stumps a 

 few millimeters in length. 



3. If specimens with partially atrophied tentacles be allowed 

 to close, the basal healthy portion of the tentacle begins to extend 

 as the internal pressure is reestablished. 



4. Atrophy of the distal portion of the tentacles occurs in 

 specimens of C. solitaries which are kept for a long time without 

 food and is also found in nearly all specimens taken during the 

 midwinter season. 



5. Since the internal pressure in normal animals is due primarily 

 to the activity of cilia any conditions which reduce the activity of 

 the cilia reduce the pressure. Low temperature and starvation 

 or exhaustion cause reduction in ciliary activity and so in internal 

 pressure. If these conditions continue for a certain length of 

 time atrophy begins at the tips of the tentacles, proceeding prox- 

 imally as the reduction in pressure continues. 



6. The fact that atrophy due to reduced pressure always begins 

 at the tip of the tentacle may be explained by the relatively greater 

 reduction in the force and volume of the circulatory currents in 

 the distal region in consequence of the smaller size of the ten- 

 tacular cavity in that region or it may be due to a condition of 

 malnutrition in the distal regions of the tentacles which in turn is 

 the result of the small size of the tentacular cavity and the dis- 

 tance from the main digestive cavity. In this condition the distal 

 regions of the tentacle are less capable of continuing their exist- 

 ence under unfavorable conditions (c. g., reduced pressure) than 

 the more proximal portions. Possibly both of these factors are 

 concerned in the result. 



HULL ZOOLOGICAL LABORATORY, 



UNIVERSITY OF CHICAGO, November, 1903. 



