336 LOUISE A. ANDERSON. 



of disintegration half way back to the mouth; (5) from the end 

 of stage 4 to completion of disintegration to the level of the 

 mouth; (6) from the end of stage 5 along the margins to the 

 posterior end of the first zooid ; (7) from the end of stage 6 to 

 complete disintegration of the first zooid. The death of the sec- 

 ondary zooids is not considered. Ten animals are usually em- 

 ployed in each test, and the number of animals in each stage of 

 disintegration is recorded hourly. The results are graphed by 

 giving to each stage a numerical value, beginning with zero for 

 stage 7. complete disintegration, and adding ten for each stage, 

 intact animals being assigned the value of 60. The numerical 

 value assigned to each stage is then multiplied by the number of 

 animals in each stage at each observation. These values for the 

 ten animals are then added together and divided by ten ; the 

 quotient thus gives the average stage of disintegration of the ten 

 animals at the particular time of observation. Thus if at one 

 observation, three animals were in stage 2, four in stage 3, and 

 three in stage 4. their values would be 100,160, and 120, respec- 

 tively, making a sum of 380; this divided by ten gives 38, or the 

 average stage of disintegration reached, at the time in question. 



i. Experiments with CJicinicals. To test the effect of alkalies 

 on susceptibility to toxic chemical solutions, it was necessary of 

 course to choose chemicals that were in themselves neutral. Anaes- 

 thetics were selected as the most convenient. Ethyl alcohol, 4 

 per cent., and chloretone, o.i per cent., were used. The anaesthetics 

 for the control set of worms were made up in ordinary well water, 

 those for the experimental set in the same water, made alkaline to 

 pH 9.0 with NaOH. The results are shown in Figs. 3 and 4, 

 being graphed according to the method explained above. Fig. 3 

 represents the results with alcohol, Fig. 4 with chloretone. In each 

 graph, the solid line is the rate of disintegration of the control 

 worms in ordinary water, the dashed line, the experimental worms 

 in alkaline water. In each case, the disintegrating action of the 

 anaesthetic is seen to be more rapid in alkaline solution. 



2. Experiments with Lack of Oxygen. When chemical agents 

 are used the question of their penetrability is involved and com- 

 plicates the interpretation of the results. For this reason it was 

 thought advisable to kill the animals by other than chemical means 



