I4 E. E. JUST. 



in the presence of blood, but they set up no reaction. In my 1917 

 series of Echinarachnius eggs, heavily inseminated with Arbacia 

 sperm, this is clearly shown in the sectioned material. Moreover, 

 these eggs are viable ; though literally studded with Arbacia sperm, 

 they are capable up to twenty- four hours later on insemination 

 with Echinarachnius sperm of giving development of a high degree 

 of normality. 



It should be noted that in these experiments clean shed sperm 

 of Arbacia was used. If the sperm be obtained from the testes 

 admixed with blood, the per cent, of cross fertilization is reduced. 

 This has been repeatedly observed. In some cases, indeed, the 

 shed sperm may give around 30 per cent, fertilization and the 

 sperm from the testes no fertilization. I believe that this is due 

 to the toxicity of Arbacia blood. This toxicity is well known 

 from Lillie's observations. I have likewise mentioned elsewhere 

 that Arbacia blood is markedly toxic for Nereis eggs. 



Similarly, mixtures of shed Arbacia sperm and shed Echina- 

 rachnius sperm exhibit no antagonism; eggs of either form or of 

 both dropped into such sperm mixtures fertilize. With mixtures 

 of sperm cut from the testes the results are different, for such 

 mixtures cut down the per cent, of cleavage. In one experiment 

 made with mixtures of shed Arbacia sperm mixed with shed 

 Nereis sperm there was no sperm antagonism, since eggs of each 

 form developed upon inseminations from the mixture. 



These, then, are the results of inseminating eggs of Echina- 

 rachnius in its body fluid or own blood. 



We may conclude: (1) Blood blocks straight fertilization. (2) 

 Blood blocks cross fertilization. (3) Blood blocks both straight 

 and cross fertilization after the spermatozoa stick to the eggs or 

 enter them and not by preventing the attachment of spermatozoa 

 to the eggs. 



These conclusions admit of certain suggestions concerning the 

 nature of specificity in the fertilization reaction. We may discuss 

 these briefly. 



III. 



The block to cross fertilization is cortical. As Lillie says : " The 

 various methods used to induce hybrid fertilization — staling of 



