Section IV., 1915 [43] Trans. R.S.C. 



The Swarming of Odontosyllis. 



By C. McLean Fraser, Ph.D. 



(From the Pacific Coast Biological Station, Departure Bay, B.C.) 



Presented by Dr. A. B. Macullum, F. R.S.C. 

 (Read May Meeting, 1915.) 



On Feb. 10, 1913, Mr. F. A. Potts of Trinity Hall, Cambridge, 

 read a paper on "The Swarming of Odontosyllis," at a meeting of the 

 Cambridge Philosophical Society, which paper appeared in the Pro- 

 ceedings on April 23, following. Observations made on Odontosyllis 

 phosphorea Moore, a species of Annelid found in the vicinity of the 

 Biological Station, Departure Bay, B.C., provided material for the 

 body of the paper, to which is added a comparison of the habits of 

 this species with that of other Syllids and Nereids. 



The observations made and recorded were of much interest and 

 the conclusions appeared to be so but as is often the case when con- 

 clusions are based on very limited observations, further examination 

 shows the necessity of considerable revision. 



As far as the phenomenon of swarming is concerned, repeated 

 observations confirm all of Mr. Potts' statements without producing 

 anything of value in addition. The time of day at which spawning 

 takes place seems definite without doubt, but definite as regards 

 the position of the sun, not definite as to the time on the clock. Very 

 few have been seen very much before sunset, but from sunset or pos- 

 sibly a little before it until almost dusk, that is for a period lasting 

 from half an hour to an hour, they appear at the surface whether the 

 sun sets early or late. 



There is nothing further to indicate that the males are attracted 

 to the females as they are in 0. enopla. In every instance each indivi- 

 dual whether male or female comes to the surface without any apparent 

 regard to the position of any other individual. The movement at the 

 surface seems just as liable to be away from as towards the nearest 

 individual of the other sex. It would therefore seem that although 

 the number of individuals is great, the chance for fertilizing all of the 

 ova, or even a large portion of them, 'is very slight. The chances might 

 be increased if the eggs were pelagic at or near the surface but they are 

 not so. They may remain suspended for some time in water that is 



