THE SIGNIFICANCE OF PALOLO 265 



annual breeding-time, and this partial failure of the worms 

 to swarm may indicate that the changing pressure due to 

 rise and fall of tide over the reefs is a contributory, but 

 not a necessary, component of the stimulus which calls forth 

 the breeding-swarm. It is more probable, however, that 

 confinement within the wood-inclosed space of the live-car 

 and the lack of perfect circulation of water acted as a partial 

 preventive of the swarming, and that the reaction is wholly 

 independent of the rise and fall of the tide. In any event, 

 it is evident that the worms can swarm normally in a 

 tideless sea, and that rise and fall of tide is not a necessary 

 or sole cause of the swarming." 



On the other hand, when the scows were provided with 

 light-tight wooden covers, so that the moonlight was kept 

 off, none of the worms swarmed. It seems, therefore, that the 

 worms require the stimulus of the moonlight. " In nature 

 the worms will swarm in overcast or cloudy weather, so 

 that even diffuse moonlight appears to be capable of calling 

 forth the breeding-season." We have here, therefore, a 

 striking instance of a constitutional change that is, so to 

 speak, punctuated by an external periodicity. 



Dr. Mayer calls attention to another very interesting 

 aspect of the phenomenon. In the Atlantic palolo the 

 annual breeding-season is only of one to six days' duration, 

 and the males outnumber the females in the ratio of about 

 three to two ; whereas in Nereis, where the breeding-season 

 is fully one hundred days long, the males greatly outnumber 

 the females. "It is evident that a shortening of the 

 breeding-season would cause a greater concentration of 

 breeding individuals, and would therefore permit of a 

 relative decrease in the number of males and a corresponding 

 increase in the number of females ; for, whenever a female 

 swarms, it is important, for the preservation of the species, 

 that there should be a male near her to fertilise her eggs. 



