BREEDING HABITS OF THE HETERONEREIS FORM 

 OF NEREIS LIMBATA AT WOODS HOLE r 



MASS. 



FRANK R. LILLIE AND E. E. JUST. 



The senior author has used the eggs of the pelagic form of 

 Nereis limbata in studies on fertilization for several years. 

 During the seasons of 1911 and 1912 collections were made each 

 night by the junior author, and records were kept which reveal 

 considerable uniformity in swarming periods in accordance with 

 the phases of the moon. In addition advantage was taken of the 

 opportunity to study certain other features of breeding behavior. 

 These observations are brought together in a paper partly for 

 the sake of such general interest as they may possess and partly 

 for the information of those w r ho may have occasion to use this 

 form for investigations. 



The animals may be taken after sunset on certain nights, in 

 general during the "dark of the moon," in the months of June, 

 July, August and September. They appear swimming near the 

 surface of the water very soon after sunset, and may be 

 attracted by the light of a lantern and readily caught with a 

 small hand net. The swarming usually begins with the appear- 

 ance of a few males, readily distinguished by their bright red 

 anterior segments and white sexual segments, darting rapidly 

 through the water in curved paths in and out of the circle of 

 light cast by the lantern. The much larger females then begin 

 to appear, usually in smaller numbers, swimming laboriously 

 through the water. Both sexes rapidly increase in numbers 

 during the next fifteen minutes, and in the case of a large swarm 

 there may be hundreds of males in sight at one time, though the 

 number of females to be seen at one time rarely exceeds ten or a 

 dozen. 1 In about 45 minutes the numbers begin to decrease and 



1 At the height of some runs, as for instance, on the evenings of June 12, July 

 5 to 8, and August 6-10, 1912 (see curves 6, 7 and i), great numbers of females 

 appeared. On one occasion at least a liter of females was secured in ten minutes, 

 several being caught with each sweep of the net. Within the circle of the light on. 

 such nights as many as fifty females may be seen at once. 



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