182 Heredity and Environment 



We have in these facts a remarkable correlation between the 

 distribution of the chromosomes and the occurrence of certain 

 characters of the adult animal. The association of maternal and 

 paternal chromosomes in fertilization and their segregation in 

 the maturation of the germ cells is parallel to the association of 

 Mendelian characters in the zygote and their segregation in the 

 gametes; if the distribution of chromosomes in cleavage is ab- 

 normal the larva shows abnormal characters (Boveri) ; sex de- 

 termination is associated with the distribution of a particular 

 chromosome to one-half of the spermatozoa, and the fertilization 

 of the egg by one or the other type of spermatozoa. (Wilson). 

 There are many parts of a germ cell, all of which may be con- 

 cerned in heredity and development, but the chromosomes appear 

 to be the seat of the differential factors for Mendelian characters. 



On the other hand it has been objected by certain investigators, 

 notably Child, Foot and Strobell, et al, that chromosomes are not 

 the causes of anything, but that they are the "results of dynamic 

 processes," "the expression rather than the cause of cell activi- 

 ties." This objection seems to confuse the idea of natural cause 

 with that of final cause. Science knows nothing of the latter; 

 any natural cause is only a link in the chain of cause and effect, it 

 is itself the result of antecedent causes and the cause of subse- 

 quent results. Undoubtedly the chromosomes are the results of 

 antecedent processes, and yet they may also be the causes of sub- 

 sequent results. No thoughtful person has ever maintained that 

 chromosomes or any other things in nature are autonomous, abso- 

 lute, uncaused causes. 



Abnormal Distribution of Chromosomes and Factors. Experi- 

 mental evidence that the chromosomes are the seat of inheritance 

 factors is found in the correlation between the abnormal distribu- 

 tion of chromosomes and the development of abnormal characters 

 in the embryo or adult. An abnormal distribution of chromo- 

 somes to the cleavage cells may be caused in a variety of ways but 

 one of the least injurious methods of accomplishing this is by 



