2/8 C. M. CHILD. 



alcohol, ether and acetone-chloroform, commercially known as 

 chloretone. The effects of all are essentially similar in kind, but 

 of course differ quantitatively according to the substance and the 

 concentration. Ether, for example, in a concentration of 0.4-0.5 

 per cent, produces about the same effect as alcohol in a concen- 

 tration of 1.5-1.6 percent. In solutions of these concentrations, 

 individuals and pieces have been kept alive as long as three months, 

 though the resistance differs greatly according to the condition of 

 the animals and various other factors, most of which can be con- 

 trolled experimentally either directly or indirectly. 



In order to avoid as far as possible decrease in concentration 

 of the solution by evaporation the following method has been 

 used. The animals or pieces are placed in Stender dishes of sev- 

 eral hundred c.c. capacity with ground edges and a cover with 

 ground groove exactly fitting the edge. The groove is filled 

 with solution of the same concentration as that in the dish so 

 that the dish is sealed so long as the fluid does not evaporate 

 from the groove. After the dishes are thus closed they are 

 placed in larger jars containing a liter or more of the same solu- 

 tion and these are sealed with vaseline and the covers weighted 



o 



so that no escape of vapor or entrance of air is possible. And 

 finally, all solutions are renewed every forty-eight hours and are 

 made up immediately before using. In this way it is possible to 

 compare the effect of the anaesthetic upon pieces of different size 

 and from different regions of the body and also upon worms in 

 different physiological condition. 



This method makes possible the control and modification of 

 form regulation in this species to a greater extent than any other 

 which has been described. At present, however, only certain 

 points will be considered, a full account of the experiments being 

 postponed to a future time. 



In several of my " Studies on Regulation " I discussed the 

 changes in shape and proportion which occur in isolated pieces 

 of various species of turbellaria and which, under the usual con- 

 ditions, constitute an approach to the shape and proportions of 

 the whole animal. These experiments \vith anaesthetics furnish 

 new data which confirm my earlier conclusions, and it is some 

 of these data which are to be presented here. 



