FERTILIZATION IN PLATYNEREIS MEGALOPS. IO7 



inseminations" : i. e., Nereis males were cut up dry and a drop of 

 the sperm without the addition of sea-water added to eggs of 

 Platynereis cut up dry. Inseminations were made in a variety 

 of ways as the following table of method shows: 



Table II. 



Summary of Inseminations made in 1911, 1912, 1913, and 1914 

 Platynereis sperm on Nereis egg. 



1. Few sperm in sea-water. Fresh eggs in sea- water. 



2. Dense sperm suspension. 



3. Few sperm in sea- water. Stale eggs in sea- water. 



4. Dense sperm suspension. 



5. Few sperm, dry, Fresh eggs dry. 



6. Heavy insemination dry. 



7. Few sperm, dry. Stale eggs washed. 



8. Heavy insemination, dry. 



Reciprocal crosses of Platynereis eggs and Nereis sperm were 

 made. 



"Stale eggs" are eggs that have stood in sea-water for several 

 hours. "Stale eggs, washed" are stale eggs on which the water 

 has been changed several times. 



These experiments were made repeatedly during four seasons. 

 The sperm of Platynereis has practically no effect on the egg of 

 Nereis whether fresh or stale, dry or in sea-water. In one ex- 

 periment (191 1) I got jelly formation in a few eggs. This ex- 

 periment later repeated (191 3) gave no result. If Nereis eggs 

 be inseminated with Platynereis sperm during the evening of 

 capture they show no change the next morning. Inseminated 

 with Nereis sperm twelve hours after insemination with Platy- 

 nereis sperm, the eggs develop normally if anything in greater 

 numbers than such stale eggs in ordinary sea-water do. 



Nereis sperm will cause Platynereis eggs to form jelly, the per 

 cent, of eggs thus responding depending upon the amount of 

 sea-water used and the density of the sperm suspension. But in 

 general many of the eggs fail to form jelly, or go through matura- 

 tion. Many that maturate do so with the cortex partially or 

 wholly intact. Sections of these eggs preserved at three minute 



