42O BENJAMIN H. GRAVE. 



temperature and ends in the fall when the water drops below 

 that temperature. It may be in order to say that this theory is 

 true only in a very general sense, since the species that have been 

 studied by me do not agree among themselves in this regard. 

 Thus Cumingia began to spawn on June 21, 1926, when the 

 temperature of the water was 60 F. and quit about September 

 25 when the temperature was 65 F. Bugula flabella at began 

 spawning on June 20 in 1926 when the temperature was 60 F. 

 and continued until November 26, when the temperature was 

 47 F. Bugula usually begins to shed its larvae by June 10 and 

 continues until late in November, which makes the discrepancy 

 in temperature less pronounced, June 10 temperature being 

 approximately 55 F., November 25 temperature 45 F. Chxto- 

 pleura begins to spawn about June 25, temperature 60 to 65 F. 

 and ends early in September, temperature 65 to 70 F. 



Spawning is caused at particular times in nature by various 

 specific stimuli and it is not determined by temperature alone. 



Orton gives convincing evidence to show that temperature is 

 the chief factor in determining the limits of the spawning seasons 

 of marine invertebrates. He, however, dismisses the factor light 

 with too little emphasis. Although most tropical animals may 

 spawn throughout the long summer in accordance with his 

 theory, the Palolo worm spawns on one or two days only; and 

 the ripening of its gametes is influenced by light according to 

 several investigators. Light plays a part both in the maturing 

 of the gametes and in spawning in several well-known cases. 

 A very striking example is Dictyota at Beaufort, N. C., as de- 

 scribed by Hoyt. Temperature, no doubt, is the chief factor in 

 determining the spawning season just as it is also the most 

 important factor in growth and all protoplasmic activity. 



SECTION II. 



ARTIFICIAL SPAWNING STIMULI. 

 /. Shock. 



As stated in my paper on Chxiopleura (BiOL. BULL., 1922), 

 certain marine invertebrate animals will spawn when placed in 

 an artificial or unusual environment, stimulated apparently by 



