428 BENJAMIN H. GRAVE. 



period of the full moon until new moon, and that the period of 

 the first quarter is the period of restricted spawning. This 

 behavior of Cumingia can scarcely be explained on any other 

 ground than as a lunar effect. 



There is no adequate way of describing the variations in 

 spawning that are so obvious to the experimenter. However, 

 the tables of data appended to this section, together with the 

 comments written at the time the experiments were performed, 

 must suffice to explain the basis of the conclusions arrived at. 

 Although they are long, there seems to be no way to give the 

 evidence more briefly. I give the data for three years only as 

 representative. 



DISCUSSION. 



There has been much speculation about the cause of lunar 

 periodicity in spawning, but it has for the most part remained 

 speculation and guessing. It can never be solved except by ex- 

 periments similar to those devised by Mayer. Neither Cumingia 

 nor Chxtopleura is suitable for a study of the causes which have 

 produced lunar periodicity. In the first place, periodicity is not 

 clear-cut in these species and in the second place they can be 

 observed only under laboratory conditions which have been 

 shown to be unreliable. They are affected by shock whereas 

 some species are apparently not so affected. 



A casual survey of known cases of lunar periodicity shows a 

 general similarity in all and it is likely that the underlying causes 

 are the same in all. A study which undertakes to explain these 

 phenomena should include a search for other cases and especially 

 all worms that are known to show a lunar periodicity should be 

 studied in detail for purposes of comparison. However, specu- 

 lation and comparison can scarcely explain it. There is need 

 for experimental methods and the Palolo worm, and the Suez 

 sea urchin or possibly Nereis limbata are among the most favorable 

 species for study. It should be a comparatively simple problem 

 to subject them to artificial light, especially polarized light, in 

 addition to all the light to which they are accustomed, to see if 

 they can be thrown out of tune. The Palolo worm seems to 

 offer the best opportunity because of its definite and predictable 



