238 B. H. GRAVE. 



checked up as far as possible by observations of their habits under 

 natural surroundings where the possibility of shock is eliminated. 

 The writer is presuming, therefore, that the spawning periods 

 of Chcstopleura are restricted to ten days in each of the summer 

 months, extending approximately from full moon to the third 

 quarter. This, however, is not set forth as a fact. If laboratory 

 data are wholly trustworthy, the spawning periods extend from full 

 moon to new moon with the qualifications noted in the text. 



CONDITIONS AFFECTING SPAWNING. 



As a matter of convenience in the study of the spawning periods 

 of Chcctoplcura, it was found most advantageous to remove the 

 animals from the shells to which they normally cling and to keep 

 them in shallow crystallization dishes. 



It was soon discovered that they spawn only at night, usually 

 beginning about 7.30 or 8 P.M. and continuing until 10.30 P.M. 

 It is not uncommon for them to spawn at intervals throughout the 

 night. 



During the day the animals were kept aerated by means of run- 

 ning water, but toward evening they were washed free from sedi- 

 ment and placed in dishes on laboratory tables. They rarely 

 spawned in running water, but the change to quiet water furnishes 

 an effective stimulus to spawning. Under these conditions one or 

 more males usually respond within fifteen minutes, females some- 

 what later. If allowed to remain in running water, neither males 

 nor females respond, so far as has been observed. It is therefore 

 evident that these animals are affected by currents of water, and 

 one naturally suspects that they spawn under natural conditions, 

 either at low or high tide when the water is slack. No convincing 

 evidence that they spawn at the time of low or high tide was 

 obtained from laboratory experiments. 



Although these animals rarely spawn in water that is strongly 

 agitated, they spawn readily in dishes which constantly receive a 

 fresh supply of sea-water, provided the inflowing stream does not 

 perceptibly disturb or agitate the water in the dish. This shows 

 that spawning is not induced by the accumulation of carbon dioxide. 

 The same conclusion may be drawn from the fact that spawning 



