CHROMOSOME COMPLEX OF SPEKMATOCYTES. 325 



characters in the individual and groups of individuals, but must 

 also offer some explanation of the possible origin of new charac- 

 ters which serve as the basis for new genera and species or, in 

 other words, of variation. The most we can hope to accomplish 

 by observation, in any event, is to determine the mechanism by 

 which the germ cells operate to produce the body structures 

 the principle back of this can only be guessed at. 



Before undertaking the formulation of any hypothesis it may 

 be well to consider a few questions concerning the nature of body 

 characters and their relation to each other and to the germ cells. 

 The term "character" has a very broad and uncertain meaning. 

 It may be applied to any structure of the organism from a vitally 

 important organ to a trivial marking on the surface of the body. 

 It is very much a question whether the characters belonging to 

 these categories are equally firmly fixed upon the germ plasm, 

 and for our present purpose it is desirable that we know whether 

 there is any relation between the need of a character and its fixity 

 in the chromosome. Again we should know the relations of the 

 characters to each other in development. We shall have to as- 

 certain, for instance, whether an organ or part develops purely 

 as a result of the presence of one particular chromosome or 

 whether the structure owes its initial stages to the action of one 

 chromosome and its later development to the influence of an- 

 other. It will be necessary to determine to what extent the 

 chromosome acts as an individual and how far it functions as a 

 mutually cooperating element in a complex. These considera- 

 tions lead finally to the question as to the nature of the individual 

 chromosome at different periods in the development of an organ- 

 ism. Is the chromosome of the just mature germ cell potentially 

 the same as that of the tissue cell in the adult organism, or has 

 the latter become progressively different throughout the ontog- 

 eny of the organism ? If the second condition obtains then it is 

 necessary to determine the means by which the chromosomes of 

 the germ cells maintain their primitive nature through successive 

 generations while the somatic cells in each acquire their various 

 characteristics. 



These considerations force themselves upon one as soon as the 

 attempt is made to establish a relation of any sort between an 



