32O L. V. HEILBRUNN. 



perform all of the experiments in low Stender dishes (containing 

 about 50 cc.) instead of in larger fingerbowls. These dishes were 

 very convenient, for they could without any trouble be put on the 

 stage of the microscope. One Stender dish was made to contain 

 the desired reagent and then the eggs were pipetted into it- 

 After varying lengths of exposure the eggs were transferred 

 from the reagent to fresh sea-water also contained in Stender 

 dishes. Then after twenty minutes or more had elapsed the 

 treated eggs were examined. 



As the polar bodies of Cumingia are unusually large it is possible 

 to count the percentage of matured eggs under low power and 

 without removing the eggs to a slide. Counts were usually made 

 in this way. Obviously it is not possible to see the polar bodies 

 if the egg is lying with the animal pole down. Hence the per 

 cent, recorded is always too low. Even if all the eggs had polar 

 bodies not many more than fifty per cent, would show them. 

 If the eggs are turned about this difficulty can of course be ob- 

 viated, but turning is a tedious process and was only occasionally 

 resorted to. Thus the counts recorded represent minima and are 

 really only about half as high as they should be. Counts are 

 given in the form of fractions, in which the denominator repre- 

 sents the total number of eggs counted the numerator the number 

 of eggs with polar bodies. For example the fraction 10/50 would 

 indicate that out of 50 eggs counted 10 showed a polar body. 



In making up per cent, solutions of volatile liquids, it was 

 found convenient to use 100 c.c. measuring flasks. Thus if a 

 2 per cent, ether solution was desired 2 c.c. of ether was placed 

 in a 100 c.c. measuring flask and sea-water was added until the 

 solution reached the 100 c.c. mark. Owing to the diminution 

 in volume on mixing the two liquids such a solution is not exactly 

 a 2 per cent. one. However, after the above method of procedure 

 it is easier to calculate the molecular concentration. 



The accompanying table gives the results of experiments with 

 eleven substances which lower surface tension. For each sub- 

 stance used it was necessary first to determine the proper con- 

 centration. Sometimes this was a simple matter. Thus for 

 saponin almost any concentration is successful. But usually 

 only a narrow range of concentrations will produce the desired 



