BREEDING HABITS OF HETERONEREIS. 153 



substance, or it ceases to be effective in the presence of a certain 

 concentration of sperm. This is shown by the following experi- 

 ment, June 20, 1911: A male put in about 8 c.c. of the water 

 charged by a female immediately shed sperm which was stirred 

 up by his movements; in a little w T hile he stopped shedding. 

 He was then transferred directly to another equal amount of 

 the original charged water and the performance was repeated. 

 A third transfer gave the same result, and on the fourth transfer 

 a small amount of sperm only was shed, the male being practically 

 spent by this time. 



The same phenomenon was observed on other occasions. The 

 explanation is, I believe, that the stimulating substance is a 

 sperm agglutinin produced by the eggs, w^hich enters into com- 

 bination with the spermatozoa and thus disappears from the 

 solution in the presence of a sufficient quantity of sperm. The 

 reasons for this opinion are: (i) The sea-water charged by the 

 female does, as a matter of fact, contain a sperm agglutinin 

 which can be shown to be neutralized by the addition of a suffi- 

 cient quantity of sperm. (2) This sperm agglutinin possesses 

 about the same degree of heat lability as the substance effective 

 in causing the sperm-shedding reaction of the male. The rela- 

 tions of the sperm to egg-secretions will form the topic of another 

 paper, but they are summarized in a preliminary paper by the 

 senior author in Science, N. S., Vol. XXXVI., p. 527. The 

 conclusion to which we have come is, therefore, that the same 

 egg-secretion of Nereis which agglutinates the spermatozoa is 

 the effective stimulus in the sperm-shedding reflex of the male. 

 This is the simplest explanation of the facts and may be held 

 until some reason is shown for believing that different substances 

 are involved. Such a condition is particularly well adapted to 

 secure fertilization under the conditions of the breeding habits 

 of Nereis. 



II. DATA ON THE "RUNS" AND THE "SWARMS." 



By a "run" we mean an entire lunar cycle of the pelagic 

 " Heteroriereis"; by a "swarm" the nightly occurrence. A gen- 

 eral statement of the facts was given in the introduction. The 

 precise data with some comparisons follow: 



