48 THE ROYAL SOCIETY OF CANADA 



With regard to the time of tide Mr. Potts says, "The tide was full 

 or just falling." This is scarcely accurate. On Aug. 15, 1911, it 

 was low tide at 14.53 and high at 21.10, on Aug. 16, low tide at 15.34 

 and high at 21.40. The 1912 tides are given in the table. Sunset 

 in the two cases in 1911 occurs well on in the rising tide and on Aug. 

 18, 1912 at about half tide on the fall. It seems more nearly correct 

 to say that the largest swarms are found at high tide or somewhat 

 before that time, as far as the area at the entrance of Departure Bay 

 is concerned (See table). A possible reason for this lies in the fact 

 that the flood tide comes in from the south. The current is divided 

 by Protection and Newcastle Islands, part going through Nanaimo 

 Harbor and Newcastle Channel to reach Departure Bay. The outer 

 current is less obstructed and as usual arrives at the north end of 

 Newcastle Island before the other current, but the distance it works 

 into the bay varies, apparently depending more upon the direction 

 and force of the wind than on any other factor. Unless the surface of 

 the water is very smooth the line where the two currents meet can 

 readily be traced across the entrance of the bay. The outside current 

 would tend to carry these annelids, coming from the deep in the Strait 

 of Georgia, forward with it until the other current meets it and as 

 there is practically still water here (the doldrums on a small scale) 

 the individuals become collected into a swarm and it is here they are 

 found the most plentifully. When the water is very smooth the area 

 may be very much extended but on ordinary occasions searching for 

 them outside of the entrance to the bay has always produced negative 

 results. This would account for the greater numbers being found on 

 the rising tide. If the water is very smooth during the height of the 

 spawning period they are probably found at any time of the tide. A 

 smooth surface seems to be one of the requisites for swarming. I have 

 never been able to find any at the surface even when the surface was 

 but moderately disturbed. After» some days of storm, they have 

 been found on the next smooth evening to be present in very large 

 numbers. It may readily be that at times during the spawning period, 

 when it has not been possible to find any or many at the entrance of 

 the bay, on account of tide and current conditions, they may have 

 drifted in some other direction and at some other smooth spot they 

 may be plentiful. 



I have no doubt since OdontosylUs is found over such a wide area 

 in dredged material, that the phenomenon of swarming occurs at other 

 places as well as at the entrance to Departure Bay, as especially among 

 the islands to the south there is an endless variety of current conditions 

 and in this variety there must be some that suit. The swarming takes 

 place at such an awkward time of the day for making observations at a 



