FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 15 



eggs, high concentration of sperm, use of alkalies or other chemi- 

 cals — have therefore this one feature in common, that they destroy 

 the chemical or physical integrity of the cortex of the egg" (Lillie, 

 '19, page 219). Specificity in fertilization thus manifests itself in 

 the cortex of the egg. 



But specificity in fertilization is not absolute, but relative. This 

 fact would seem to indicate that the results of straight and of 

 cross fertilization are due to quantitative, not qualitative, differ- 

 ences in the cortical response to insemination ; species sperm more 

 readily than foreign sperm overcome the same resistance to ferti- 

 lization set up by some cortical substance or condition. The ques- 

 tion, therefore, comes down to this: What in the cortex is re- 

 sponsible for the block to fertilization, whether by species or 

 foreign sperm? 



In the first place, most methods used to induce cross fertilization 

 in echinids hasten the loss of fertilizin. Thus staling is an easy 

 method for the removal of fertilizin. Eggs allowed to stand or 

 repeatedly washed lose their fertilizin content. Washing the eggs 

 rapidly with dilute sea-water brings about a loss of fertilizin. 

 Dense sperm suspensions rapidly bind available fertilizin. I ven- 

 ture the opinion that heat hastens the loss of fertilizin also. 



If, now, we postulate that specificity in fertilization is wholly 

 due to the presence of fertilizin, then must we also take the next 

 step, namely, that cross fertilization is most successful when the 

 fertilizin is reduced? That is, fertilizin is necessary for straight 

 fertilization, but a block to cross fertilization; certain kinds of 

 artificial parthenogenesis (heat, for example, on Nereis egg) de- 

 pend upon the presence of the fertilizin in maximum concentra- 

 tion; certain eggs lose their capacity for fertilization by species 

 sperm very rapidly (Platynereis) ; but with foreign sperm the case 

 is otherwise — it can fertilize after an egg is no longer capable of 

 response to artificial stimulus or that of species germ. But might 

 not specificity in fertilization be accounted for in part on the basis 

 of the data presented in this paper? This would mean at least 

 with the knowledge at hand that specificity in fertilization is due 

 in part to the blood, since the presence of blood blocks fertilization 

 by species or foreign sperm. 



