PHYSIOLOGY OF RECONSTITUTION OF PLANARIA LATA. 121 



head frequency by means of chemical agents have been performed, 

 but are only briefly mentioned. 



The data on respiration include comparative estimations of C0 2 

 production by colorimetric determination of pH with phenol-sul- 

 phone-phthalein as indicator and the indicator-buffer solutions 

 made up by Hynson Westcott and Dunning as standards. In 

 these experiments lots of as nearly as possible equal weights of 

 animals or pieces to be compared are sealed in pyrex tubes of the 

 same diameter as the standard tubes in equal volumes of indicator 

 solution of the same concentration as the standard tubes and the 

 change in color recorded at regular intervals and usually also to a 

 definite pH. Some data on oxygen consumption determined by 

 the Winkler method are also given. For these I am indebted to 

 the kindness of Dr. Hyman. 



In the experiments on susceptibility KNC has been chiefly used 

 as agent, since it has been abundantly demonstrated that with 

 proper precautions susceptibility to KNC can be used as a general 

 comparative measure of physiological condition and particularly 

 of rate of respiration in Planaria. 1 In the present study the sus- 

 ceptibility method has been used for two purposes : first, for dem- 

 onstration of the axial gradients and the posterior zooid by the 

 differential susceptibility of different levels of the body; second, 

 to demonstrate the changes in physiological condition of pieces 

 following section. The general susceptibility gradients are shown 

 in figures and the comparative susceptibilities of pieces by graphs. 

 The method of graphing the data is described in connection with 

 the data. 



In the experiments on reconstitution the body posterior to the 

 head is cut into a certain number of pieces — four, six, eight, 

 sixteen — according to the experiment. Animals of the same size 

 are used for each experiment and the pieces from each individual 

 are cut as nearly as possible the same length, the more extreme 

 irregularities being discarded. Consequently the corresponding 

 pieces from different individuals represent as nearly as possible the 

 same region of the body. All corresponding pieces — i.e., those 



i Child, '14a, c, '15a, chaps. III.-VII., '16, '19a, b; Hyman, '19a, b, c, '20, '22. 



