2Q4 ELLINOR HELENE BEHRE. 



ferentiated enough, for the purpose of these experiments. Congo 

 red and benzo-purpurin were not very satisfactory because they 

 were taken up by the slime secreted by the worms so that the 

 color in the solution itself became so varyingly diluted as to 

 make accurate comparison uncertain. Liquid litmus and phenol- 

 pthalein were used to some extent; but by far the most satis- 

 factory for the purposes of these experiments was the phenol- 

 sulphonepthalein used by Haas (1916) which combined all of 

 the desirable qualities for a good indicator non-toxicity, slow- 

 ness of the penetration rate, great sensitiveness to very slight 

 increase in H-ion concentration, and a suitable working range 

 from PH 8.6 to PH 6. The starting point for these experiments 

 was of course the PH of the well water in which the worms lived 

 in the laboratory about PH 7.6; but this point is not very 

 significant for the purposes of these experiments as no attempt 

 was made to determine the absolute PH but rather the com- 

 parative changes in PH in terms of color differences. 



In the earlier experiments equal numbers of worms of the 

 same size were compared without weighing. Later, beginning 

 with series XXV., and throughout the rest of the experiments, 

 the worms were weighed and the weights recorded; and an at- 

 tempt was made to put the excess weight now on one side, now 

 on the other, so as to prevent the weight from being by any 

 possibility the determining factor in the results. The worms 

 were weighed in water at the temperature at which they had been 

 living in each particular case. A small glass container with the 

 water was first quickly balanced, and the worms were placed in 

 this after a moment on filter paper to remove excess water. 

 After weighing they were placed in pyrex tubes of standard 

 volume; these were rinsed and then filled with indicator solution 

 and sealed, with air excluded by paraffined corks, or, better 

 paraffin plugs. The worms were then put into the new tem- 

 perature away from the direct sunlight and all other strong 

 illumination in order to preclude the possibility of stimulation 

 from those sources. To avoid as far as possible the differences 

 in motor activity resulting from differences in temperature the 

 worms were decapitated, (except in a few cases indicated in the 

 table), shortly before weighing. At any time from ten minutes 



