SPECIFICITY IN FERTILIZATION 197 



nomena were essentially similar to dispermy or poly- 

 spermy within the species: aster-formation from each 

 sperm nucleus, a tetraster or polyaster first cleavage, 

 abnormal development, and early death. The lack of 

 specificity in the events between penetration and cleav- 

 age is thus clearly shown. Kupelwieser, however, 

 concludes that all kinds of spermatozoa possess the 

 same chemical stuff for activation of eggs, an erroneous 

 conclusion which we shall now consider. - 



Discussion: These rapidly reviewed data on echi- 

 noderm hybridization demonstrate in an entirely con- 

 vincing manner the existence of non-specific factors in 

 fertilization; and they also demonstrate with equal 

 clearness the existence of specific factors. The latter 

 are found first in the cortical reactions, which never 

 occur with equal facility in crosses outside the genus, 

 and second in the latest stages of fertilization after 

 union of the germ nuclei. Apparently any spermato- 

 zoon that has once crossed the barrier of the egg cor- 

 tex calls forth the same set of events within the egg. 

 The sperm aster is evidently a non-specific reaction, 

 and when this system is once set in operation it can 

 continue in only one way so long as it is not impeded 

 by incompatibilities of another kind. 



As to the specific factors there is unquestionably 

 resistance at the periphery of the egg, which is most 

 promptly and readily overcome by the species sperm. 

 In the interspecific crosses of sea urchins there is not a 

 strong cortical resistance, but the quantitative studies 

 necessary for an evaluation of the specific factor have 

 not been made in this case. When we come to inter- 

 generic and wider crosses within the order we find that 



