■172 C. M. CHILD. 



interpretation of the reduction processes as reversals of develop- 

 ment (Lillie, Schultz and others). It is evident from my experi- 

 ments that the individuals reduced by starvation, although they 

 may be simpler morphologically, than the full-grown individuals, 

 are physiologically not younger but older than these. 



IX. Length of Life. 



In an extended series of experiments I have attempted to col- 

 lect data concerning the length of life in anaesthetics of constant 

 concentration, with the result that some conclusions of interest 

 have been reached. 



As noted above, young individuals of small size are more sen- 

 sitive than older, larger, and die in greater numbers during the 

 first two or three days, but if they survive this period they very 

 commonly Hve longer than the larger older animals, since they 

 become more completely acclimated. Pieces from the posterior 

 region of the body of large animals and corresponding to the sec- 

 ond zooid behave in the anaesthetics like young animals. 



Animals and pieces which have been well fed up to the begin- 

 ning of the experiment live longer in anaesthetics than starving 

 individuals and pieces. It is of interest to note that the further 

 starvation advances, the earlier do the animals die in anaesthetics 

 of given concentration. 



Pieces from different regions of the body show very different 

 degrees of resistance to the anaesthetics. Pieces from the anterior 

 region without the head live much longer than pieces of the same 

 length from the middle region. Short pieces including the old 

 head die much earlier than longer pieces and their death is not due 

 to reduction in consequence of starvation to the limit of existence, 

 for they die long before such reduction occurs. In other series of 

 experiments pieces have been allowed to begin the process of regu- 

 lation in water and have been placed in the anaesthetic at various 

 stages. If we compare long and short pieces with anterior ends 

 at the same level of the body, we find in general that, as regula- 

 tion proceeds, the short pieces, which have undergone a more 

 extensive reorganization than the long pieces, behave more and 

 more like young animals when placed in the anaesthetic, i. e., they 

 are more sensitive at first, but if they survive they become more 



