EGG-LAYING IN AMPHITRITE. 265 



is probably due to interference with excretion, caused by clogging 

 the nephridial sacs with eggs. 



Undoubtedly much the same process occurs in other worms 

 where eggs accumulate in nephridial sacs before oviposition. 

 I am told by Downing that eggs accumulate before oviposition 

 in the nephridial pouches of one species of Arenicola. Gerould 

 has reported that the eggs of Phascolosoma collect in this way 

 for several hours before they are laid, and there is little doubt 

 that the same general method of egg-laying occurs in all worms 

 with this habit. My results may be summarized in the following 

 conclusions. 



1. The separation of ccelomic corpuscles and unripe eggs, at 

 the time of oviposition in Amphitrite, is accomplished by physical 

 not chemical means. 



2. The work of cilia on the fimbriated membrane furnishes 

 the power used in the separating process. Wave-like contrac- 

 tions of the body aid in expelling the eggs, and it is suggested 

 that these movements are due to interference with excretion, 

 caused by clogging the nephridial sacs with ripe eggs. 



3. The separating process is aided in several ways. The 

 shape and arrangement of grooves on the fimbriated membrane, 

 the size and shape of the bodies separated, and especially the 

 greater plasticity and greater density of the mature eggs, all 

 appear to be important factors in separating the bodies found in 

 the ccelome at the time of oviposition. The action of the grooves 

 in closing over a ripe egg is also a direct help in keeping other 

 bodies from the main groove. 



4. We are fairly safe in concluding that the method of egg- 

 laying described for Amphitrite holds good for other worms where 

 the eggs accumulate in nephridial sacs before or during oviposition. 



