JOHN W. SCOTT. 



Again, the nephridia are not extraordinarily large, and each 

 must be refilled many times in the course of one oviposition 

 where thousands of eggs are deposited. Nor do the nephridia 

 ever seem to be entirely filled with eggs ; at least such is the 

 case in worms that are killed almost instantly with hot sublimate 

 acetic while in the act of oviposition. The meaning of this will 

 appear in the explanation. It is also manifestly clear that the 

 movements of the body referred to before, cause the body con- 

 tents to move forward toward the diaphragm. As a rule, each 

 effective contraction-wave stops a short distance posterior to the 

 nephridia and holds for a moment the compressed ccelomic con- 

 tents in the much distended anterior portion of the body. Dur- 

 ing the final part of a contraction-wave, a stream of eggs oozes 

 out a short distance from each nephridiopore posterior to the 

 diaphragm. The contraction movements, therefore, are neces- 

 sary for the expulsion of the eggs. 



The explanation which I believe accords best with all the 

 known facts is as follows : First, it should be remembered that 

 the nephridial sacs always occupy a lower position with reference 

 to gravity than the nephrostome, whether the worm lies in a 

 horizontal or vertical direction. We may then think of the 

 nephridia as settling basins in which the heavier products are 

 drawn off from the bottom after a certain amount has accumu- 

 lated. Ciliary action undoubtedly would prevent lighter objects, 

 such as the ccelomic corpuscles and the unripe eggs from set- 

 tling in the basin ; and when a sufficient quantity of the ripe eggs 

 (heavier objects) have accumulated, pressure from the strong 

 contraction-wave forces them through the nephridiopore. The 

 separating process probably takes place during relaxation, be- 

 tween contraction waves. Owing to the opacity of the worm's 

 body, it is impossible to actually observe this process, but all of 

 the facts point to this simple explanation. 



SUMMARY. 



I. In Amphritite oruata Verrill, the egg-laying reflex is closely 

 associated with the time of spring tide ; the height of any given 

 period of egg-laying always occurs within two days of the time 

 of new or full moon. Periods of oviposition occur in June, July 

 and August. 



