EGG-LAYING IN AMPHITRITE. 263 



then thrown across the groove and against the pillars where 

 the currents hurriedly lift them up and drive them away. I did 

 not see a blood corpuscle pass down the main groove into the 

 nephridial pouches, so long as the cilia retained their normal 

 activity. After an hour or so their action becomes slower, but 

 this is probably due chiefly to the fact that much plasma has 

 evaporated . 



The Separation of Immature from Mature Eggs. The small, 

 immature eggs, Fig. I, b and c, as well as some of a larger size 

 are eliminated in much the same way as blood cells. The task 

 grows more difficult, however, as the eggs increase in size for 

 they become too bulky to be bounced off the edge of the mem- 

 brane like the blood cells. So, as the larger immature eggs (Fig. I , 

 d) are carried into the narrowing grooves, they are rolled up on 

 edge, then lifted out and moved away. For when the sides of 

 the groove narrow down so that both sides of the flat egg are 

 affected by the currents produced by cilia on the opposite sides 

 of the groove, the combined action of these currents is sufficient 

 to lift even the weight of a large, immature egg. The case 

 is different with the mature eggs, which differ in shape, are more 

 plastic, and are somewhat heavier than most immature eggs found 

 in the ccelome. These eggs are carried into the grooves down 

 which they slowly pass, their shape and weight evidently being 

 such that the lateral cilia are unable to lift them out of the groove. 

 Undoubtedly their plasticity is also an important factor in 

 resisting the action of the cilia. The side of the egg gives before 

 the effective stroke of the cilia, so the result is to change the 

 shape of the ripe egg rather than to push it away, and conse- 

 quently such eggs move more slowly along the grooves. In 

 some cases it was observed that the folds of membrane along the 

 sides of the groove would respond to the presence of a ripe egg 

 by folding over, virtually forming a closed tube. Inside this 

 tube-like groove the egg could occasionally be seen changing 

 shape, as it was forced slowly along toward the nephridial sac. 

 When the membrane folded it was impossible for unripe eggs, 

 or corpuscles on the membrane, to pass into the nephridial pouch 

 with the ripe egg. The behavior of the membrane in the pres- 

 ence of a ripe egg had all the appearance of a tactile response. 



