192 HEREDITY AND SEX 



of sea water plus 8 cc. of 2^2 NaCl), the development 

 may be carried through. 



Loeb concludes that the oxidations set up in the egg 

 by a change in its outer surface affect the egg itself 

 injuriously; and unless they are removed or the 

 effects are counterbalanced by some other change 

 (as when a hypertonic solution is used) the egg goes 

 to pieces. Hence he believes that the sperm has a 

 double r61e in fertilization. First it changes the surface 

 layer and increases in consequence the oxidations 

 in the egg ; second, the sperm brings into the egg some 

 substance that counteracts poison produced by the 

 oxidation itself. 



This is what fertilization accomplishes from a 

 physiological point of view. In addition, we have 

 seen that fertilization brings into the egg certain ma- 

 terials whose presence affects the characters of the 

 individuals that develop from it. This is what fertili- 

 zation does from the point of view of the student of 

 heredity. 



Let us turn for a moment, in conclusion, to the 

 question of sex of animals that come from artificially 

 parthenogenetic eggs. 



In natural parthenogenesis such eggs may de- 

 velop into males, sexual females, or parthenogenetic 

 females. 



But in artificial parthenogenesis the egg has already 

 undergone reduction in its chromosomes and is repre- 

 sented by half of the female formula as far as the 

 chromosomes are concerned. The half formula will 

 be XABC for the type with homozygous female. 

 Since the egg has one X it may be expected to become 



