BREEDING HABITS OF PLATYNEREIS MEGALOPS. 



203 



I have never taken this Heteronereid at Woods Hole earlier 

 than June 29. In 1911 I remained at Woods Hole until Septem- 

 ber 18; I took no worms after August 24. For 1913, August 19 

 is the date of last capture. 



The following tables selected from data of 1911, 1912 and 1913 

 give some idea of the lunar periodicity of the swarming : 



TABLE I. 1911. 



(Date of first capture, July 20.) 



Comparison with Nereis shows in the first place that the num- 

 ber of worms swarming is not so great. It was found, for 

 instance, in collecting Nereis to be practically impossible to make 

 an accurate estimate of the number of males; for that reason a 

 record was kept of the females only. On two or three nights only 

 did I find it impossible to estimate the number of Platynereis 

 males swarming; on other evenings it was easily possible to 

 count them. The swarm of males on the evening of August n, 

 1912, was wonderful. For a few minutes the sea was alive with 

 thousands of the rapidly swimming Heteronereids. In 1913 

 there was a similar swarm of females, but in no such numbers. 

 As in the case of Nereis the collections were made in one place 

 during the three years. 



The season, moreover, appears to be shorter than that of 



