EARLY DEVELOPMENT OF POLYCHOERUS 

 CAUDATUS, MARK. 



EDWARD G. GARDINER, Ph.D. 



This worm, first described by Mark (i), may be found in 

 abundance in the waters of Woods Holl harbor and vicinity. 

 During the summer months it lives on the eel-grass and on 

 dead shells in shallow water. In the northwest gutter of 

 Hadley Harbor, where there are extensive sand and mud flats 

 covered by but a few inches of water at low tide, large num- 

 bers of dead shells of clams, pectens, and mussels are scattered 

 over the surface. On the under and thus darkened side, these 

 beautiful little red worms collect in quantity, often as many as 

 a dozen on one shell. That they prefer the dark is evident 

 even when placed in a clear glass dish on a table near the win- 

 dow, as they invariably congregate on the surface away from 

 the light ; or if a small portion of the dish is shaded they seek 

 the darkest corner, crowding close together and often one on 

 top of another to secure a position sheltered from the light. 

 Also if shells are placed in the dish they cluster on the lower 

 and thus shaded side of the shell. They seem to prefer a 

 clean, fresh shell, and are to be found more frequently on the 

 shaded surface of a white clam shell than on that of those 

 darkened by age and marine growths. 



It is on these sheltered portions of their favorite abiding 

 places that the eggs are to be sought, for when kept in a 

 glass dish they lay their eggs quite freely. It is noticeable, 

 however, that the eggs are more frequently deposited on the 

 under surface of a shell, if there be one in the dish, than in 

 the light ; also that they lay more frequently in the night than 

 in the day-time if no place sheltered from the light rays is 

 offered to them. That it is darkness rather than the hour of 

 night which induces them to deposit their ova, is shown by the 

 following experiment at the season when they were laying 



