30 GENETICS 



size between the egg-cell and the sperm-cell, in hered- 

 ity the two are practically equivalent, as has been 

 repeatedly shown by making reciprocal crosses be- 

 tween the two sexes. The only features that are 

 apparently alike in both the germ-cells are the 

 chromosomes. The inference is, therefore, that they 

 contain the determiners which are the causal factors 

 for the equivalence of adult characters in heredity. 

 The existence of an extra chromosome in probable 

 connection with the matter of sex is, as will be pointed 

 out later, an exception to the exact chromosome 

 equivalence of the two sexes, which only goes to 

 strengthen the supposition that the chromosomes are 

 the carriers of hereditary qualities since extra chromo- 

 somes are always associated with the character of sex. 



Second: The process of maturation, which always 

 results in halving the chromosome material of the 

 germ-cells as a preliminary step to fertilization, is 

 a series of complicated manoeuvers not practised by 

 other cells. During this process no other part of 

 the cells appears to play so consistent and important 

 a role as the chromosomes. Provided they act as 

 hereditary carriers, their peculiar behavior during 

 maturation is just what is needed to bring together 

 an entire complement of hereditary determiners out 

 of partial contributions from tw^o parental sources. 



Third : Sometimes abnormal fertilization occurs, as 

 in the case when two or more sperm-cells, instead of 

 one, enter the egg cytoplasm and unite with the egg 

 nucleus. This unusual performance has been artifi- 

 cially induced by chemical means in the case of sea- 



