FERTILIZATION IN PLATYNEREIS MEGALOPS. 97 



- . I drop. 



No. I 



.... 2 drops. 



2 



3 ' 



4 4 



5 : 5 



6 ' 



10 c.c 



7 



no sea- water. 



8 



The worms were then cut up and flooded with sea-water, later 

 transferred to fresh sea-water in finger bowls. 



Nos. I, 2, 3 and 8 gave cleavage; a per cent, of normal trocho- 

 phores was found the next morning. In dishes 4, 5, 6 and 7 not 

 an egg divided, no swimming forms developed. 



No single observation in the whole work was made as often as 

 this- the results are wonderfully precise. As I shall show later 

 the experiment quoted was conducted under the optimum con- 

 ditions, and yet it shows the inhibiting effect of such a surpnsmgly 

 small quantity of sea-water. All other observations show two 

 drops of sea-water for each worm to be the maximum that will 

 permit normal fertilization. In no case have I got cleavage where 

 two and one-half drops of sea-water for each worm (i. e., five 

 drops to two worms) were used. While the same pipette was used 

 to secure equal drops, the worms, females particularly, vary m 

 size I have usually taken the average females for these experi- 

 ments. Such an animal, as found by actual count in three cases, 

 has about 11,000 eggs. There is enough variation, however, in 

 the size and weight of the worms to make impossible any law 

 concerning the lethal amount of sea-water. I believe, never- 

 theless, that there is an optimum time for the addition of sea- 

 water— equal to the time the sperm are in the female in normal 

 insemination; and an optimum amount of sea-water— about as 

 much as the worms will take up after thorough drying. 



The results of these inseminations over a period of four seasons 

 prove clearly that sea-water except in minute quantity is fatal 

 to fertilization. 



Does Sea-water Injure Egg, Sperm, or Both? 



Three explanations of the failure of Platynereis eggs to cleave 

 after insemination in sea-water are possible: 



