EGG-LAYING IN AMPHITRITE. 255 



against possible error caused by surface tension, the material 

 was placed between two solutions of differing densities and then 

 centrifuged. But surface tension did not appear to offer any 

 appreciable resistance to the passage of the eggs and corpuscles 

 either upward or downward. It was found that eighty turns of the 

 hgematocrit in one and one half minutes was sufficient to produce 

 thorough separation of materials in the capillary tubes, without 

 noticeably affecting the material within the egg membrane. This 

 amount of centrifuging was therefore adopted throughout the 

 entire series. I shall here present in order my findings in regard 

 to (i) the specific gravity of eggs, (2) the specific gravity of cor- 

 puscles, and (3) the specific gravity of sperm, together with 

 remarks as to the significance of these results. 



After a number of preliminary experiments, in order to get 

 familiar with the method to be used and to guard against possible 

 sources of error, a series of tests was made upon eggs recently 

 deposited. The results of some of these tests are shown in 

 Table I. The female used in this series was found depositing 



TABLE I. 

 To SHOW THE SPECIFIC GRAVITY OF RECENTLY DEPOSITED Amphitrite EGGS 



eggs in a normal manner. Just as quickly as it could be done, 

 while they were still being deposited, these eggs were centrifuged 

 with the results shown in tests 25 to 30 inclusive. The table 

 shows that the specific gravity of recently deposited, that is, 

 mature Amphitrite eggs, lies between 1.075 an d 1.085. They 

 probably have a mean density very near 1.078; for almost all 

 eggs remain on top of, and therefore are lighter than a solution 

 with a specific gravity of 1.080, while more than half sink in a 

 solution with density at 1.0775. Tests were made on eggs from 

 other worms and verified the results given here. 



