THE BIOLOGY OF THE CELL SURFACE 



mosomes maintain their individuality. The hnear arrange- 

 ment of the genes in each chromosome^ is the same for the 

 given chromosome whether it is in a fertihzed egg, in a kid- 

 ney-cell, a muscle-cell or any other cell of the adult organ- 

 ism. Now at each cell-division though the chromosomes 

 are split they must somehow maintain their identity or 

 individuality; this maintenance is the prevailing doctrine 

 among geneticists. 



Speaking of the individuality or genetic continuity of 

 the chromosomes, Wilson says": 



In any general account of the history and genetic relations 

 of the chromosomes in the life-cycle, we inevitably find our- 

 selves speaking of them as if their identity were really lost 

 when they disappear from view in the resting or vegetative 

 nucleus. The vast literature of the subject is everywhere 

 colored by the implication that chromosomes, or something 

 which they bear, have a persistent individuality that is 

 carried over unchanged from generation to generation. This 

 view has met with some determined opposition; but with tlie 

 advance of exact studies on the chromosomes escpticism 

 has gradually yielded to the conviction that the chromo- 

 somes must, to say the least, be treated as if they were per- 

 sistent individuals that do not wholly lose their identity at 

 any period in the life of the cell but grow, divide and hand 

 on their specific type of organization to their descendants. 

 This does not mean that chromosomes are to be thought of 

 as fixed and unchangeable bodies. Beyond a doubt they 

 undergo complex processes of growth, structural transfor- 

 mation and reduction, in some cases so great that no more 

 than a small fraction of the substance of the mother- 

 chromosomes at its maximum development is passed on to 

 the daughter-chromosomes. Whether we can rightly speak 

 of a persistent "individuality" of the chromosomes is a 

 question of terminology. What the facts do not permit us 

 to doubt is that chromosomes conform to the principle of 

 genetic continuity; that every chromosome which issues 

 from a nucleus has some kind of direct genetic connection 



^ Delage, iSg^, p. 731, very clearly expressed the idea of a linear 

 arrangement in the chromosomes. 

 2 Wilson, 1925. 



322 



