January 14, 1916] 



SCIENCE 



51 



That the fertilizable condition arises sud- 

 denly has been shown especially by the 

 work of Delage on the starfish egg and of 

 "Wilson on the egg of Cerehratulus. Their 

 experiments on merogony showed that parts 

 of the full-grown ovum taken prior to the 

 rupture of the germinal vesicle are incapa- 

 ble of fertilization ; but, soon after the rup- 

 ture of the germinal vesicle, parts, whether 

 nucleated or not, readily fertilize. Hert- 

 wig's observations (1877) also showed a 

 complete failure of the fertilization reac- 

 tion in primary ovocytes of the sea-urchin 

 before rupture of the germinal vesicle, even 

 when spermatozoa penetrated. I have ob- 

 served the same thing in Chcetopterus. 



(b ) Eggs of Platynereis lose their capac- 

 ity for fertilization almost immediately 

 after coming into sea water, even though 

 spermatozoa may penetrate (Just) ; eggs of 

 the frog become unfertilizable after half 

 an hour in water (Spallanzani) ; eggs of 

 the wall-eyed pike completely lose their fer- 

 tilizability after ten minutes in water 

 (Reighard). Usually fertilization capacity 

 begins to faU off in one or two hours after 

 eggs are laid in most marine animals, 

 though in some, as in the sea-urchin, it may 

 persist much longer. 



(c) Once fertilized eggs do not fertilize 

 again, nor do parts of such eggs freed of 

 the fertilization membrane. It should there- 

 fore be impossible to superimpose parthe- 

 nogenesis and fertilization; and the stud- 

 ies of Mr. C. R. Moore, one of my students 

 (not yet published), show this to be the 

 case. Apparent superposition appears in 

 all cases to be due to incomplete reactions, 

 which cease and may be subsequently re- 

 sumed. The fertilization reaction appears 

 to be irreversible; and the appearance of 

 reversal in parthenogenesis may be re- 

 ferred, like superposition of fertilization on 

 parthenogenesis, to incompleteness of the 

 initial reaction. 



Specificity is an outstanding feature of 

 the fertilization reaction, the significance 

 of which is not weakened by any hybridiza- 

 tion experiments. "We need not stop to de- 

 fine the limits nor the consequences of hy- 

 bridization in order to justify the assertion 

 that no theory of fertilization which fails 

 to include the factor of specificity as one 

 of the prime elements can be true. 



The fundamental character of specificity 

 is illuminated by the phenomena of self- 

 sterility; in species where this occurs the 

 eggs and sperm of the same individual are 

 sterile inter se, though fertile with those 

 of all other individuals. This has led some 

 botanists to the conception of individual 

 stuffs; but Correns's experimental analysis 

 led him to the conclusion that the specific 

 factor is not an individual stuff, but a def- 

 inite combination of stuffs for each indi- 

 vidual. The combination arises always 

 with the individual, and disappears with it. 

 An extension of the principle of self -steril- 

 ity is found in that mutant of fruit flies dis- 

 covered by Morgan in which the males and 

 females are fertile with other mutants, but 

 sterile inter se. The only biological par- 

 allel of such phenomena is found in the in- 

 dividual blood composition revealed by ser- 

 ological studies. That there is a common 

 factor in species and individual specificity 

 studies no one who has studied both sets 

 of phenomena can doubt. 



A consistent theory of fertilization must 

 take account of all these phenomena, not 

 only the internal factors of maturity of 

 germ-cells and the specificity of their reac- 

 tions, but also the external factors that 

 favor or inhibit the reaction. I have at- 

 tempted to show in a series of papers that 

 the fertilizable condition of the egg de- 

 pends upon the presence of a specific sub- 

 stance which is produced at the time of 

 rupture of the germinal vesicle and which 

 disappears completely after fertilization. 



