426 BENJAMIN H. GRAVE. 



There is no clock-like regularity in the spawning of Cumingia 

 in nature. Not all individuals spawn promptly at the full moon. 

 Spawning in fact covers a period of two or three weeks in each 

 month. We know this by the quantities of eggs spawned in the 

 laboratory by any particular lot of sexually mature adults 

 brought in. Some set free a maximum quantity, some a small 

 quantity and some only a few eggs or none at all. The last are 

 considered to have spawned recently. By this indirect reasoning, 

 one learns that there is no one particular day on which general 

 spawning occurs. It is likely that spawning occurs when the 

 gonads and their ducts become filled to capacity and this internal 

 pressure no doubt constitutes a second natural spawning stimulus. 

 If the production of gametes were continuous, and uniform in 

 rate, spawning might occur on any day in the month except for 

 this cosmic stimulus which brings about a more or less marked 

 rhythm. I am of the opinion that there is a rhythm in the rate 

 of production of the gametes as well as in the spawning of them. 

 In any case, the only time in the month during which most of 

 the gonads seem empty and during which spawning stimuli seem 

 to be suppressed is the period of the first quarter. Beginning at 

 full moon the heavy spawning is sometimes completed before 

 new moon but more frequently not until near first quarter. In 

 many respects Cumingia resembles Toxopneustes, the Beaufort 

 sea urchin, whose periodicity was described by Tennent. The 

 production of gametes in this species is rapid and the gonads 

 are soon replenished after spawning occurs. 



It should be noted here that there is a distinction between 

 stimuli which bring about the act of spawning and those which 

 bring about the maturing of the gametes. The latter may be an 

 evenly continuous process or it may be enhanced at certain 

 times. The former is merely the act of extruding these gametes 

 and may be induced by some external stimulus, such as those 

 due to the moon in its various phases, or to any other external 

 stimulus. 



In the following paragraphs I give the history, of this study of 

 Cumingia as constituting an important part of the experimental 

 basis for the conclusions drawn. 



During the greater part of the breeding season of Cumingia, 



