H. M. FucHS 289 



7 °l^ more than did the Strong ylocenU'otus extract. As the other 

 three comparisons in the Table show an equal effect of the two extracts 

 this difference is probably due to an error in the experiment. 



TABLE XXX. (2.30..^ and 3.9.6.) 



strong 

 Water e 



1 cc. sperm 40 88 95 



Strongt/locentrotus Echinus 

 Water extract extract 



■r. , r, ■ . ,, ( 1 CC. sperm 



Exp. 1. Stroiuiylocentrotus Ah { 



( 3 cc. sperm 62 96 95 



■r, , .. , ,,,, ( 3 drops sperm 13 25 26 



h,xp. 2. Stroiiqiiloceiitwtus C a ■ , 



^ ^■' ' ( 1 cc. sperm 29 78 77 



4. Comparison of the effects of Strongylocentrotus and Echinus egg- 

 extracts on the fertilizing power of Echinus sperm. 



In the following experiment Strongylocentrotus and Echinus extracts 

 were again used, but in this case a comparison was made between their 

 effects on the fertilizing power of Echinus sperm. Definite equal 

 amounts of Echinus sperm (see Table XXXI) were pipetted into 

 (1) 6 cc. water, (2) 5 cc. Strongylocentrotus egg-extract, and (3) 5 cc. 

 Echinus egg-extract. To each was then added .5 cc. water, and they 

 were poured on to separate equal quantities of Echinus eggs. Table 

 XXXI shows that both extracts had the same effect on the Echinus 

 sperm. 



TABLE XXXI. (-2.31. .5.) 



strongylocentrotus Echinus 

 Water extract extract 



Echinus B/c 



•6 cc. sperm ... 41 79 78 



2 cc. sperm ... 66 84 83 



5. Comparison of the effects of Strongylocentrotus and Echinus egg- 

 extracts on the fertilizing power of Strongylocentrotus sperm, used to 

 fertilize Echinus eggs. 



The experiments detailed in the preceding sections have shown 

 clearly that the fertilizing power of sperm-suspensions is as much 

 increased by treatment with egg-extract from another species as it is 

 by an approximately equal concentration of the egg-extract of the same 

 form. Evidently then the specificity of fertilization can in no way be 

 due to any differential effect of egg-secretion from the same and from 

 other species, and the cause of the general difficulty of effecting inter- 

 specific hybridizations must be sought for elsewhere. 



Now, suppose two species, X and Y, which hybridize with com- 

 parative ease. Fi'om what has just been said, it would be expected 



Journ. of Gen. iv 19 



