178 U.S. NATIONAL MUSEUM BULLETIN 2 27 



spawning season but may attain a relatively largo size before doing so ; 

 thus they may attain a length of 200 mm. The length of life does not 

 normally exceed 18 months and includes only 1 breeding season. 



The early development has been followed by Dales (1950). The 

 eggs are lecithotrophic. The larvae develop in the mud and there is 

 no true pelagic phase, although young individuals may be whirled 

 up in the water and thus be found in the plankton. They developed 

 into ciliated monotrochophores, then into free-swimming larvae 

 with limited swimming powers. By 7 weeks they were 1.6 mm. long, 

 with 10 setigerous segments, and feeding began. During the first 8 

 weeks, the larvae developed in the parent burrow and by 10 weeks 

 were 4 mm. long, with 20 setigers, and pigmented. They were minia- 

 ture adults, burrowing in the mud and constructing minute U-shaped 

 tubes. The worms grew rapidly and steadily increased in length 

 during the first summer after hatching, increasing 10-20 mm. in length 

 each month; young worms hatched in February reached a length of 100 

 mm. by October, During the winter months, there was little or no 

 increase in length. The germ cells grew rapidly during this period. 

 By October in the female, the coelom contained small oocytes; the 

 coelom became filled with a loose parenchyma tissue which appeared 

 to be responsible for the growth and deposition of yolk in the oocytes. 

 The loose parenchyma disappeared and mature oocytes came to fill 

 most of the coelom. In the male, the loose parenchyma soon dis- 

 appeared; "sperm -plates" formed and acquired tails; free sperm were 

 found in the coelom for two weeks before spawning. In both sexes, 

 histolysis of the muscle layers of the body wall took place and it 

 became very thin by the time spawning was ready to take place, 



Boguchi (1954) cultivated N. diversicolor in the laboratory aquar- 

 ium (temperature 15° to 20° C). They reached sexual maturity and 

 reproduced in the spring breeding season; young animals 6 months 

 old reached the length of the adult animal (about 100 mm.). 



Material examined.- — Numerous specimens from Gulf of St. 

 Lawi'ence (Bay of Haha, Saguenay River, St, Lawrence estuary, 

 Cascapedia River, Port Daniel, New Richmond, Bay of Chaleiu-s), 

 Nova Scotia (shore opposite Five Islands, east side Cape George, 

 Delap Cove, Kingsport), New Brunswick (New Horton), Maine 

 (Starboard Creek in Machias; Drummore Bay at Phippsburg; Rob- 

 binston on St, Croix River; Boothbay Harbor region, Sheepscot and 

 Cod Cove, Sheepscot River, off Merrill Ledge, North Edgecomb, 

 Fort Popham; gut between Sawyer and Barter Islands, cove south 

 shore Sawyer Island, Sagadahoc Bay and Riggs Cove, Georgetown 

 Island, Medomak; Bradstreet Cove off Poorhouse Cove, John's 

 River), New Hampshire (Oyster River just below dam in stream bed; 

 Beard's Creek emptying into Oyster River near Durham, Emerson's 



