EREANTIATE POLYCHAETA OF JAPAN. 181 



5. — The swarming invariably takes place just after the flood- 

 tide in the evening. 



6. — The swarming continues generally from one to two 

 hours. 



7. — (3n warm cloudy nights, the swarming seems to take 

 place generally in larger scale than on clear chilly nights. 



As to the tidal conditions in the mouth of the Sumida 

 Kiver during the two months of October and November, it is 

 known : 



1) that spring-tides occur in the evening within three days 

 following the day of the new and the full moon ; and 



2) that the spring-tide following the new moon is higher than 

 that after tlie full moon. There is then noticeable a parallelism 

 between the occurrence of the densest swarm and the highest 

 spring-tide during the months concerned. Noteworthy seems also 

 the fact that in the present species the time of swarming closely 

 follows both the new and full moons. 



Family Syllidae. 



Body very slender, definitely segmented, nnd often with arti- 

 culated tentacles and cirri, the former and some of the latter 

 being occasionally very long. 



rrostomium, rounded or quadrangular, with 3 tentacles (a 

 m('di;iii and (wo laterals) and usually 1 eyes. Palpi generally 

 prosciil in various degrees of dcvulopment and separation. 

 reristomiiini wlWi tentacular cirri, rarely with bristles. The 

 mouth followt'd liy pharyngeal cavity, and then by the pro- 

 trusil)le i)roboscis (Pharynx, Schhmdrohre) with chithious wall, 

 which organ in situ is often sinuous and rarely straight. In its 



