ZOOLOGY: F. R. LILUE 
157 
addition of a sufficient quantity of an accurately determined sperm 
suspension stirred in quickly to reach the desired dilution. The final 
dilution is then made in the presence of eggs, and the age of the final 
dilution is therefore practically zero with reference to the fertihzation 
reaction. 
Under these conditions 100% of the eggs may fertiHze up to a dilution 
of about 1/3000 of a 1% sperm suspension. The curve of fertihzing 
power of the sperm suspensions measured in terms of the percentage of 
eggs fertilized then falls off slowly to 1/24,000 of 1% sperm, then rapidly 
to about 1/300,000%, then slowly again to about 1/90,000,000% where, 
however, about 1% of fertilization may still take place. Accompanying 
observations showed that beyond a dilution of about 1/5000 of a 1% 
sperm suspension only a single spermatozoon can possibly be concerned 
in the fertihzation of each egg. 
One obtains exceedingly contrasting results if a series of sperm dilu- 
tions in powers of 2 is made, beginning with 1%, by first transferring a 
certain amount of the 1% suspension to a second crystal of the series and 
adding an equal amount of sea-water, proceeding similarly from crystal 
2 to crystal 3, and so on down the series. In such a case one finds that 
fertihzation rims out absolutely from about a 1/64 dilution of 1% sperm 
suspension to 1/1024% in different cases. No comment is needed to 
emphasize the contrast. 
As many as 20 to 40 active spermatozoa are found in association with 
each egg at 1/128%, which may be, however, absolutely ineffective. So 
that in an experiment running out in the seventh crystal of the series it 
would appear that a greater number of spermatozoa than this is required 
to fertihze an egg. 
These results suggest at first glance that the order of adding eggs and 
sperm to the sea- water may be of significance. This is, however, not 
the case. The repeated handling of the sperm in successive half dilu- 
tions is also not the main cause for the result. Thus it would appear 
that the only real difference between the fertihzing power of the sperm 
in these cases is a time factor. In the first case the final dilution is made 
in the presence of the eggs; in the second case 20 to 30 minutes is con- 
sumed in the preparation of the sperm dilutions before the eggs are 
added. 
The time factor is the real explanation as will be shown immediately. 
But at first sight this did not seem a very reasonable explanation for the 
following reasons: In the first place the time involved has never been 
considered sufficient to reduce fertilizing power of sperm; and in the 
