INITIATION OF DEVELOPMENT IN NEREIS. 9 



During the afternoon of July 15 this experiment was repeated 

 with the same results. 



{b) July 22. Eggs warmed at 34° C. in serum plus sea-water 

 (serum from the bodies of seven spent females cut up in two c.c. 

 of sea-water) : 10 drops plus three c.c. sea-water, 10 drops plus 

 five c.c. sea-water and 10 drops plus ten c.c. sea-water. 



Eggs exposed for twenty-five minutes. Less than one per 

 cent, developed in any dish. 



During August these results with serum eggs were verified. 

 The highest per cent, of swimming forms obtained was one per 

 cent.; this was with a very dilute serum. Not only do the eggs 

 fail ^o cleave but fail in the great number of cases even to form 

 jelly. In some cases the development of eggs inseminated in 

 serum was farther advanced than the serum warmed eggs. 

 Since in the case of the initial experiments the worms were cut 

 up in sea-water, it may be that failure of a percentage of eggs to 

 cleave is due to the inhibition of the escaping blood and tissue 

 juice. With the dry eggs cut quickly on the dry watch glass this 

 escaping juice cannot so easily contaminate the eggs. 



4. The Experiments with Washed Eggs. 



In Platynereis sea-water definitely destroys the fertilizing power 

 of the egg. Even minute quantities of sea-water will render the 

 egg incapable of cleavage although the spermatozoa may pene- 

 trate. Moreover, if the eggs of one female remain in a small 

 quantity of sea-water, 5 c.c, for instance, for thirty seconds their 

 fertilizing power is lost. And yet in nature, inseminated eggs 

 begin to be laid in many cases five or six seconds after copulation 

 (see Just, '14). In Nereis, therefore, it was thought that washings 

 in sea-water by frequent changes through several hours might 

 act as the sea-water does in such a surprisingly short time on 

 Platynereis eggs. 



During the June Nereis run, then, as many experiments as 

 possible were conducted to determine the " fertilizable " period by 

 inseminating at intervals eggs that had remained in sea-water 

 with and without frequent washings. Lillie has shown for 

 Arbacia eggs that the capacity for being fertilized decreased with 

 the decreased secretion of fertilizin. He finds for Nereis also 

 very much the same relationship. 



