THE FER T I LIZA TION-REACTION 



water for ten minutes.^ Where copulation takes place 

 between male and female before egg-laying and insemination 

 outside of the female's body, the fertilizable condition may 

 pass off rapidly. Thus, in eggs of the minnow, Fundulus 

 heteroclitus, a bony fish, the fertilizable condition is at its 

 height as the eggs extrude during the time, when as the male 

 clasps the female, spermatozoa are shed. If one removes 

 the female during the act of copulation, then gently presses 

 her in order to obtain eggs and places these in sea-water, 

 one finds that with residence in sea-water the eggs' capacity 

 for fertilization diminishes. The normally shed and insemi- 

 nated eggs show one hundred per cent, fertilization. The 

 most interesting case illustrative of a brief duration of ferti- 

 lizability is that of the eggs of Platynereis, fertilized within 

 the female's bodv. 



The male and female of this marine worm go through a 

 most peculiar type of copulation. ^ The sexually mature 

 animals swim at the surface of the sea at night during the 

 period from full to new moon of the breeding season (sum- 

 mer months) and are easily captured. In the laboratory, 

 by bringing a male and a female together in a vessel of sea- 

 water, one can observe more closely the normal behavior 

 displayed at the surface of the open sea. The rapidly 

 swimming male entwines the less active and larger female 

 and thrusts his tall into her jaws. She thus takes up the 

 spermatozoa which pass from buccal cavity to pharynx and 

 through lesions in the wall of the pharynx into the coelom 

 where they become attached to the eggs. The eggs are 

 Immediately laid. In one set of observations on 87 females, 

 I found, with the aid of fellow workers who recorded the 

 time, that the whole process, from the moment that the 

 male entwined the female to the beginning of egg-laying, 



1 Reighard, iSgj. 

 - Just, 191 4. 



189 



