IV.] FOUNDATION OF A THEORY OF HEREDITY. 241 



also proves that the assertion mentioned above is correct, for 

 the eggs which ripen first and are therefore first laid, would 

 have been fertilized had the queen been impregnated. The 

 supposition that, at certain times, the queen produces eggs 

 requiring fertilization, while at other times her eggs develope 

 parthenogenetically, is quite excluded by this experiment ; for 

 it follows from it, that the eggs must all be of precisely the 

 same kind, and that there is no difference between the eggs 

 w^hich require fertilization and those which do not. 



But does it therefore follow that the quantity of germ-plasm 

 in the segmentation nucleus is not the factor which determines 

 the beginning of embryonic development? I believe not. It 

 can be very well imagined that the nucleus of the ^g^^^ having 

 expelled the ovogenetic nucleoplasm, may be increased to the 

 size requisite for the segmentation nucleus in one of two ways : 

 either by conjugation with a sperm-nucleus, or by simply 

 growing to double its size. There is nothing improbable in 

 this latter assumption, and one is even inclined to enquire why 

 such growth does not take place in all unfertilized eggs. The 

 true answer to this question must be that nature generally 

 pursues the sexual method of reproduction, and that the only 

 way in which the general occurrence of parthenogenesis could 

 be prevented, was by the production of eggs which remained 

 sterile unless they were fertilized. This was effected by a loss 

 of the capability of growth on the part of the egg-nucleus after 

 it had expelled the ovogenetic nucleoplasm. 



The case of the bee proves in a very striking manner that the 

 difference between eggs which require fertilization, and those 

 which do not, is not produced until after the maturation of the 

 Qgg, and the removal of the ovogenetic nucleoplasm. The in- 

 crease in the quantity of the germ-plasm cannot have taken 

 place at any earlier period, or else the nucleus of the ^gg would 

 always start embryonic development by itself, and the egg 

 would probably be incapable of fertilization. For the relation 

 between egg-nucleus and sperm-nucleus is obviously based 

 upon the fact that each of them is insufficient by itself, and 

 requires completion. If such completion had taken place at an 

 early stage the egg-nucleus would either cease to exercise any 

 attractive force upon the sperm-nucleus, or else conjugation 

 would be effected, as in Fol's interesting experiments upon 



R 



