EREANTIATE POLYCHAETA OF JAPAN. 167 



one period In sting a few days ; and the period begins on the 

 night just Ijefore the day of the new or the full moon in the 

 middle or the latter part of the month mentioned. It in- 

 variably takes place in the midnight just after flood-tide. Very 

 rarely the swarming occurs in two periods, close to the consecutive 

 new and full moons. 



The swimming worms may be easily captured either with 

 tlu^ tow-net or hand -net. The native fishermen, who capture them 

 in quantities for tlie manure, employ " pyramidal net," a kind of 

 large bag net, which is stretched so as to receive the swarm 

 of the worms coming down along with the ebbing water. 



The mature worms can be easily kept alive for a 

 week or more in shallow wooden vessels placed at a shaded 

 place and containing a small quantity of water taken during 

 high tide and just enough to cover the worms. The water 

 must be changed at least once a day, taking care to remove all 

 the injured worms as soon as possible, without which precaution 

 the water will soon become so filled with discharged sexual pro- 

 ducts as to be detrimental to tlie health of the worms. Too 

 much water, as also too much light, induces the worms to mo- 

 tion and thus increases the chance of their receiving injuries to 

 the body. 



Development : - Artificial fertihzation can easily be eflfected, 

 [)i()\i(led i)recaution be taken to keep the water at a con- 

 stant temperature (al)out 15' C) and its salinity the same as at 

 liigh tide in Kojiiiia (lulf. 



About IK) minutes after fertilization, the first polar body is 

 extruded : ihr second follows about ?A) minutes later. 



The cleavage of the egg is total and unequal. The first 

 cleavage takes place abc)ut three hours after fertilization (woodcut 



