AN ANALYSIS OF THE SPAWNING HABITS AND 

 SPAWNING STIMULI OF CHJETOPLEURA 



APICULATA (SAY). 



B. H. GRAVE, 

 WABASH COLLEGE. 



The phenomenon of periodicity in the spawning activities of 

 animals has attracted wide attention since its most striking example 

 was made known in a series of papers by Collin, Kraemer, Fried- 

 lander, Izuka, and Mayer ('97 '08). These papers give the results 

 of careful studies of the spawning habits of the Palolo Worm and 

 show that both the Atlantic and Pacific species shed their gametes 

 during particular phases of the moon and tides. The time of their 

 swarming is so definite that it may be predicted as certainly as an 

 eclipse. 



Since these papers were published a distinct periodicity in the 

 time of spawning has been revealed for a number of animals, 

 related not merely to season, but to the time of the month. Many 

 animals have long been known to spawn regularly at a certain time 

 of the day or night. This paper does not deal with the problem of 

 such diurnal periodicity, but only with lunar periodicity. Most of 

 the animals which are known to exhibit a periodicity of the latter 

 category are annelids, and the degree of perfection of their peri- 

 odicity varies with that which is just discernible, as in Nereis 

 dumerilii, to that of the Atlantic palolo, Eunice fucata, in which 

 the swarming is restricted to a certain phase of the moon once a 

 year. This curious phenomenon is not restricted to animals, but 

 is shown quite as perfectly by the brown alga, Dictyota dichotoma, 

 as described by Williams ('05), Hoyt ('07), and Lewis ('10). 

 Some other species of the Dictyotacese also show a similar perio- 

 dicity in the time of freeing their gametes. 



PERIODICITY IN CH^ETOPLEURA. 



When an attempt was made, in the summer of 1919, to obtain 

 the eggs of Chcetopleura apiculata for embryological study, it was 



2,34 



