SEGREGATION OF HOMOLOGOUS CHROMOSOMES 483 



a note (which apparently Voinov has not seen) in which he 

 identifies as a supernumerary the element that he had formerly 

 reported as the accessory. 



Payne found what he believes to be a sex group in Gryllotalpa 

 borealis. That is, an accessory and an unequal pair, the larger 

 member of which always moves to the same pole as the accessory. 



McClung has recently been able, through a knowledge of the 

 J-sbaped tetrads, to solve the puzzle of the multiple in Mermeria 

 where he reported ('05), p. 316 that, "Entire tetrads pass into 

 the second spermatocytes." It is now evident that the accessory 

 is associated with a J-shaped tetrad which divides in the usual 

 manner. Since apparently the accessory always attaches to the 

 telomitic dyad, there would seem to be formed a sex-linked associa- 

 tion comparable in end results with Payne's interpretation of con- 

 ditions in Gryllotalpa borealis, the difference being that a physi- 

 cal union is lacking in the latter case. Voinov \s figures of his 

 XY pair (plate 24, fig. 29, see my text fig. 3, 6) strongly suggest 

 the association of a third element with a normal tetrad; making 

 this a true hexad multiple. A study of Wilson's figures of 

 idiochromosome pairs suggests that they also might be hexad 

 multiples; i.e., that the X is the accessory plus one dyad of a 

 tetrad of which the homologue is the Y. Since we know tetrads 

 composed of unequal homologues exist, there is no reason ap- 

 parent why the accessory might not be associated with either 

 the larger or smaller member. This might account for instances^ 

 in Drosophila, where the Y is larger than the X. This ex- 

 planation of the known facts would seem simpler than that of 

 Wilson (Tl), who attempted to derive all from a primitive X-Y, 

 pair. 



It may be well to note the bearing of the evidence as to the 

 time of segregation brought out by this work on Bateson's 

 'Reduplication hypothesis.' Bateson ('15) in a study of the 

 sweet pea found coupling of two pairs of factors which he rep- 

 resents by the formulae A a and B b, giving the heterozygote r 

 A a B b. The zygotic ratios obtained in F 2 showed that cer- 

 tain combinations between these factors occur more frequently 

 than others. This led Bateson to postulate the theory that 



