H. M. FucHS 299 



forms being sometimes as widely different as Ascidians and Echinoderms. 

 The factor in the egg-secretions, then, which increases the fertilizing 

 power of the sperm, has no connection with the specificity of the fertili- 

 zation process. It may well be that this specificity is due to the " iso- 

 agglutinins" of Lillie — that for a spermatozoon to fertilize an egg, there 

 must be a reaction between it and the iso-agglutinin of the egg, the 

 visible effect of which is agglutination. 



In the one point in which Lillie's experiments and my own coincide 

 there is complete disagreement. All my experiments have shown that 

 treatment of a sperm-suspension with egg-secretions, or with substances 

 artificially extracted from the eggs, increases the fertilizing power of the 

 suspension — that after this treatment more spermatozoa can fertilize 

 eggs than before the treatment. Lillie, however, states that there is a 

 loss or diminution of the fertilizing power of the sperm as an effect of 

 the egg-extract. Special experiments were made on the exact lines as 

 those of Lillie (see p. 275), but they too gave the invariable result, — the 

 fertilizing power was increased. I am therefore at a loss to explain this 

 after-effect on the sperm described by Lillie for his experiments. 



The end result of my own investigations is that eggs of Ascidians and 

 of Echinoids secrete substances into the sea-water in which they lie. 

 These substances increase the fertilizing power of sperm-suspensions. 

 If a sperm-suspension of a certain concentration be taken and divided 

 into two equal portions, to one of which is added some plain sea-water, 

 and to the other an equal amount of sea-water containing egg-secretions, 

 the latter portion can fertilize more eggs than can the former. Further, 

 the egg-secretions of a foreign species increase the fertilizing power to 

 an exactly equal extent as those of the same species, provided they are 

 equally concentrated. This increased fertilizing power of sj)erm-suspen- 

 sions was shown for a number of ordinary intra-specific cross-fertilizations 

 and for one case of hybridization. 



In conclusion, it should be pointed out that the conditions in nature 

 must be somewhat different from those in the laboratory. For as the 

 substances in question are secreted by the eggs lying in water, the 

 secretions must be continually washed away by currents and wave 

 action. It follows that at a small distance from the surface of the egg 

 the secretions will be present in the water only in minimal concentra- 

 tions. The action on the spermatozoa must therefore take place on, or 

 at a very small distance from, the surface of the egg. 



