SPAWNING HABITS OF CH^ETOPLEURA APICULATA. 239 



frequently begins within a few minutes after the animals have been 

 placed in quiet water, and that it is practically over before the sur- 

 rounding water is greatly affected by respiration. During the sum- 

 mer of 1920, at the height of the breeding season, a few females 

 spawned in strongly agitated water. This occurred only once 

 (July 8). 



The number of eggs obtained from one female varies from about 

 three hundred to three thousand, the average number being about 

 sixteen hundred. As a rule only a few eggs are obtained during 

 the first night after the animals have been collected. The greater 

 number of females spawn the second night. A few spawn also 

 during the third and fourth nights, but usually not to any consid- 

 erable extent. 



SPAWNING STIMULI. 



Soon after being placed in quiet water the males begin to emit 

 sperms in a double stream which soon become dispersed as clouds 

 throughout the containing dish. The females respond more slowly 

 after from one to three hours. One is therefore likely to suppose 

 that something is expelled with the sperm which serves to stimulate 

 the females to extrude their eggs. 



This phenomenon was noted by M. M. Metcalf ('92) while 

 studying two species of Chiton in aquaria. It was also described 

 by Harold Heath ('05). F. R. Lillie and E. E. Just ('13) showed, 

 without question, that in the case of Nereis limb at a a substance is 

 expelled with the sperm which is an effective stimulus to the female 

 to shed her eggs promptly. In similar manner they found that the 

 males will not shed their sperm except in the presence of a female 

 which contains mature eggs or when placed in a dish of sea-water 

 in which a mature female had been allowed to remain for an hour 

 or more. 



In order to test the assumption that this is also the case in 

 Chcctoplcura, twenty mature individuals were washed thoroughly 

 with fresh water and isolated in finger bowls of sea-water. Dur- 

 ing the night three of these females spawned and six males shed 

 sperms in quantity, thus showing that neither males nor females 

 derive any stimulus essential for spawning from the opposite sex. 

 It is evident that the females were not induced to spawn by the 



