174 PROBLEMS OF FERTILIZATION 



are not formed and the spermatozoa do not penetrate 

 into the egg, although they are numerous and active. 

 Other samples of plasma did not inhibit so strongly, and 

 very wide individual variation with reference to this effect 

 was found, which is possibly due to variation in the 

 state of maturity of the gonads. The same principle 

 holds also for the starfish; thus in a series of dilutions 

 of the coelomic fluid of the starfish, 10 per cent, 20 

 per cent, 40 per cent, 80 per cent, 100 per cent, the 

 percentages of segmentation following fertilization of 

 the eggs of the same species were 62 per cent, 43 per 

 cent, 50 per cent, 32 per cent, 26 per cent, n per cent; 

 in sea-water 98 per cent of the control eggs segmented. 

 If one takes Asterias eggs which are resistant to 

 fertilization in sea-water, a condition often found, the 

 addition of Arbacia coelomic fluid may prove very bene- 

 ficial, as the following experiment shows: a series of 

 six watch glasses was laid out containing 5 c.c. of the 

 following: (i) sea-water (control), (2) 5 per cent fil- 

 tered plasma of Arbacia in sea- water, (3) 10 per cent of 

 the same, (4) 20 per cent of the same, (5) 40 per cent 

 of the same, (6) 80 per cent of the same. Equal quan- 

 tities of active Asterias sperm were then added to each, 

 and in three minutes equal quantities of Asterias eggs 

 which had stood one hour in sea-water to allow them to 

 reach the most favorable stage for fertilization. The 

 percentages of eggs that segmented were (i) o, (2) 90 

 per cent, (3) 90 per cent, (4) 40 per cent, (5) 10 per 

 cent, (6) o. In (4), (5), and (6) membranes formed 

 though the eggs did not segment. This experiment 

 was typical of many performed. The reciprocal experi- 

 ment was not tried. 



