xiv] OBJECTIONS 217 



by them, but GREGORY points out that this conclusion does 

 not necessarily follow, very probable though it may be. 

 He writes "Although the fact that the duplication of the 

 chromosomes has been accompanied by a duplication of the 

 series of factors may seem at first sight to suggest a definite 

 connection between chromosomes and factors, yet, on the 

 other hand, the tetraploid number of chromosomes may 

 be nothing more than an index of the quadruple nature of 

 the cell as a whole. The case is, in fact, exactly analogous 

 to the ordinary zygotic cell, which has 2x chromosomes and 

 in which each factor is represented twice." 



Additional evidence, some of it of very great importance, 

 will be given below in support of the hypothesis that the 

 behaviour of the chromosomes in the maturation of the 

 germ-cells is responsible for the segregation of Mendelian 

 characters, but first it will be advisable to consider some of 

 the difficulties by which the hypothesis is faced. These may 

 be grouped in two classes, first those raised by cytologists, 

 and second those arising from the facts of genetics. 



The cytological objections that have been raised against 

 the hypothesis are of several kinds. Some observers deny 

 the existence of any such individuality in the chromosomes 

 as is required by the hypothesis. If the individuality theory 

 is false, the hypothesis that the chromosomes determine the 

 segregation of Mendelian characters necessarily falls with it, 

 but the facts and arguments in favour of the existence of 

 some sort of individuality have been considered in the pre- 

 ceding chapter, and no further discussion of them is required 

 here. A second objection that has been raised is that 

 although the main facts already described are admitted, it 

 is maintained that when the chromosomes come together 

 in pairs before the maturation divisions, they do not merely 

 come into contact and then separate as complete units in 



