BREEDING HABITS OF HETERONEREIS. 1 49 



If the animals are to be kept over night for work the next day, 

 they should be placed in separate finger bowls, preferably one 

 for each individual, but in any case never mixing the sexes. If 

 then the bowls are placed in a cool place, as on a water table 

 with water flowing around them, a considerable proportion of the 

 females and all of the males will retain their sexual products over 

 night, and the eggs may be fertilized as desired. One great 

 advantage of Nereis for experimental work is that each swarming 

 individual is always fully mature, and contains no immature 

 sexual elements whatever. 



I. The Causes of the Sperm-shedding and Egg-shedding 



Reflexes. 



An incidental observation of the senior author put us on the 

 track of the immediate cause of the sperm-shedding reflex. It 

 should be noted that males retain the sperm very tenaciously as 

 a rule, even after days in the laboratory. One day a male was 

 dropped accidentally in a bowl of sea water which had previously 

 contained a female. He immediately began to shed sperm, and ' 

 swam round and round in the bowl very rapidly casting sperm 

 until the entire 200 c.c. was opalescent. This suggested that the 

 eff'ect of the presence of the female upon the male was exerted 

 not through sight or touch, but through some chemical stimulus, 

 and a few simple experiments demonstrated this conclusiv'ely. 



If a ripe female be kept in a finger bowl containing about 125 

 c.c. of sea-water for several hours, the water will usually be found 

 to be charged with a substance which immediately incites the 

 sperm-shedding reflex of the male. Thus on June 17, 1911, the 

 following test was made with about 125 c.c. of sea- water in which 

 a female had been kept over night. A small quantity of this 

 charged sea-water was placed in a Syracuse watch crystal, and a 

 male was dropped in (8:15 A.M.); at once he shed sperm. He 

 was then returned to fresh sea-water and ceased shedding. At 

 10:30 he was again dropped into a watch crystal of the charged 

 sea-water and again shed sperm; in a few seconds he ^nafl*rans- 

 ferred to fresh sea-water, and he ceased shedding sperm. Again ^ 

 at 2 :o7 he was transferred to another supply of the charged 

 sea-water, and again shed sperm. Returned to fresh sea-water 



