STUDIES OF FERTILIZATION. 2J 



It will be seen from experiments 2 and 7 that at 15-16 C. the 

 unshaken eggs have practically full fertilization capacity up to a 

 3O-second exposure to butyric acid and that the transition to the 

 unfertilizable condition is very sudden thus between 30 and 45 

 seconds (Exp. 7) and between 30 and 60 seconds (Exp. 2). This 

 transition coincides with the onset of membrane formation and 

 all eggs that have formed membranes fail to fertilize. This is 

 well known from previous experiments, but it is not generally 

 recognized that many eggs that fail to form membranes also 

 become unfertilizable. Thus in experiment 2c after 60 seconds 

 exposure to butyric acid 15 per cent, of the eggs failed to form 

 membranes, but only 4.9 per cent, of all eggs segmented after 

 insemination. In experiment 7 this comes out even more clearly : 

 30 per cent of the eggs failed to form membranes in 7& (after 

 45 seconds exposure) and only 0.2 per cent, of all eggs segmented 

 after insemination. 



If the eggs be shaken within about 2.V-2. minutes after transfer 

 to sea-water the soft membranes are destroyed ; there is however 

 a rapid transition from this soft condition of the membrane to a 

 hard condition in which it is difficult to destroy the membranes 

 by shaking. Rather complete destruction of membranes in the 

 soft condition is accompanied by extensive agglutination of the 

 eggs, some, however, remaining free. Agglutination of the eggs 

 is indeed a fair index of the degree to which the membranes have 

 been destroyed. 



When the membranes are thus destroyed there is a slight in- 

 crease in the percentage of eggs that segment after insemination 

 as compared with unshaken eggs (cf . Exp. 2, d, e; Exp. 3 ; Exp. 

 8). The percentage is in any case exceedingly small, and the 

 impressive fact is that in all cases over 95 per cent, of the eggs, 

 indeed generally over 99 per cent, of the eggs, are incapable of 

 segmenting after insemination. Although the percentage is so 

 small it must, I think, be admitted as possible that there is a small 

 percentage of eggs that have formed membranes that still possess 

 the capacity of segmenting after insemination. In other words, I 

 think that this small percentage of segmenting eggs is not neces- 

 sarily to be referred to eggs that failed in the membrane reaction, 



