280 



THE AMERICAN NATURALIST [Vol. XLIX 



fashion, namely, 



/Fertilizin 

 gg \Spermatozoon 

 since the engulfing of the spermatozoon into the egg is a 

 physical process which bears no relation to either possi- 

 bility. 



It has been stated that the " fertilizin theory " explains 

 also the phenomena of artificial parthenogenesis just as 

 well as any other theory. In a recent book on artificial 

 parthenogenesis the writer has given the results of a 

 large number of experiments and he has tried to explain 

 some of them; the reader would, however, vainly look 

 for a ''theory" of artificial parthenogenesis. A theory 

 in a scientific sense consists in the presentation in 

 mathematical or numerical form of a phenomenon as 

 the function of its variables. The writer has tried to pre- 

 pare the ground for such a treatment of the phenomena 

 of fertilization and of the first development of the egg by 

 working out those variables which permit a quantitative 

 treatment, but even if the exploration had been advanced 

 further than it actually has been, it would not be possible 

 to ever expect that a single theory could cover all the 

 phenomena of fertilization and development, since under 

 these two headings so many physically and chemically 

 different processes are included (of which one follows the 

 other) that they can not be covered by one theory. It is 

 true the writer had in former publications occasionally 

 used the term " lysin theory of fertilization " but only to 

 express the fact that cytolytic agencies induce membrane 

 formation and that the membrane formation induced by a 

 spermatozoon might also be due to a cytolytic agency con- 

 tained in the spermatozoon ; but he has dropped this term 

 in his recent book on the subject. 



While the writer does not desire to enter into a further 

 discussion of the side-chain theory of fertilization he 

 wishes to point out that it rests on the claim that that 

 substance which causes sperm agglutination is contained 



