234 Studies in the Pkysiology of Fertilization 



2. Length of time that eggs and sperm lie in water before fertiliz- . 

 ation. 



The next factor investigated was the length of time the eggs and 

 sperm lay in water before they were brought together. The eggs and 

 sperm of one individual and the eggs of another were removed separately 

 from the genital ducts and fertilizations were made at definite intervals 

 after these genital products had been brought into the sea-water. 



The exact procedure in Exp. 1 was as follows : 



The genital products were removed at 2.55 — 3.10 p.m. : at 3.45 — 

 3.50' the first fertilizations were made. A certain quantity of eggs A 

 was placed in water, after which 3 cc. of a thick .sperm-suspension a 

 was added. At the same time an approximately equal quantity of eggs 

 D was placed in 10 cc. water in another dish and 1 cc. of a dilute sperm- 

 suspension a was added. In the previous section it was shown that a 

 considerably greater concentration of sperm is necessary to effect self- 

 fertilization than would cross-fertilize 100 % of foreign eggs, and 

 therefore the sperm a used for cross-fertilization with eggs D had to 

 be made much more dilute than that used to self-fertilize eggs A. The 

 details just given were repeated exactly at each subsequent fertilization, 

 the times of which are given in the Table below. The same sperm- 

 suspensions were of course used to effect the self- and cross-fertilization 

 after each interval. 



The other four experiments were carried out on the same lines as 

 Exp. 1. The details of the quantities of sperm and water used and the 

 intervals at which the fertilizations were made are given in Table V. 



As in all the experiments dealing with self-fertilization, more trials 

 were made than the successful ones I'ecorded below, owing to the fact 

 that there are always a certain number of individuals in which none of 

 the eggs will self-fertilize. In this series, five successful experiments 

 are recorded, but besides these there were three in which the self- 

 fertilization percentages were nil throughout. 



The first point brought out by the experiments of Table V is that 

 in every case the percentages of eggs self-fertilized rose with succeeding 

 fertilization.s. In four cases it fell again after having reached a maximum, 

 but in Exp. 3 at 4^ hours after removing the eggs and sperm from the 

 animal the maximum had not yet been reached. The corresponding 

 cross-fertilizations with the sperm from the same animals showed in no 

 case a rise in percentages with successive fertilizations. In Exps. 2 



' The fertilization times given in Table V were taken at the end of eacli operation, 

 which occupied 3 — 5 minutes. 



