REPRODUCTION 81 



ble. The human egg is approximately a sphere 

 with a diameter, in the case of a large exam- 

 ple, of about one fifth of a millimeter, and with 

 a specific gravity about that of water ; conse- 

 quently its weight must be about 0.004 of 

 a milligram. The volume of the chromosomes 

 in a fertilized mouse egg has been determined 

 to be somewhat less than one thousandth of 

 the volume of the whole egg, and, assuming 

 that this proportion hold for the human egg, 

 and that its chromosomes have about the same 

 specific gravity as water, the weight of this 

 material would be about 0.000,004 of a milli- 

 gram. Yet this minute amount of substance 

 is believed to determine to a nicety that infin- 

 ity of adult traits wherein a man resembles 

 his parents. If we assume the weight of the 

 average human being to be sixty-five kilo- 

 grams, then the weight of the determining 

 material to that which is determined is as 1 to 

 16,250,000,000,000. In attempting to grasp 

 this almost inconceivable relation, it must be 

 borne in mind that the material of the chromo- 

 somes in the egg is living and that, in the 

 growth of the individual, it assimilates and in- 

 creases in volume like other living material ; 

 it is not spread through the growing body in 



