DISTRIBUTION OF THE CHROMOSOMES 23 



produced in the male organism) will contain chromosomes 

 A and B, some A and C, some A and D, some B and C, some 

 B and D, some C and D (see Fig. 16). The same will of 

 course happen in the case of the ova (sexual cells produced 

 in the female individual). As far as we know, it appears to 

 be a matter of chance as to which sperm joins with which 

 ovum, and it seems impossible that such a combination 

 would always occur as to ensure that the new organism 

 should again contain A, B, C, and D. There are many other 

 possible combinations, and there is only one chance in six of 

 this particular combination occurring again in an organism 

 with four chromosomes. In man, where there are thirty-two 

 chromosomes, there is only one chance in 601,080,390 of the 

 same combination occurring again. In both cases even 

 these chances involve the assumption that the chromosomes 

 are the same in both parents. If they are not, the chances 

 would be more remote (see Fig. 16). With regard to those 

 characters, therefore, which always occur in every individual 

 of a species, it appears quite impossible that different char- 

 acters should be contained in different chromosomes. Taking 

 a concrete example hairiness of the scalp a constant char- 

 acter in the case of the human animal. Now suppose that 

 this character is contained in chromosome A, the number of 

 individuals in whom chromosome A was missing would be 

 25 per cent, according to the laws of chance in the first 

 generation produced from parents who all possessed chromo- 

 some A. But this character is a constant character, and the 

 number of individuals occurring who, during the whole of 

 their lives, fail to develop any hair upon the scalp is so 

 small that it is not worth considering. It would appear, 

 therefore, that if a character common to the race is present 

 at all in the chromosomes, it must be present in each of 

 them individually ; otherwise it must be present in some 

 other part of the cell, or is a common potentiality of the 

 whole substance of the cell. 



But this leaves two complicated phenomena without any 

 ostensible function. If the common racial characters are. 



