SEGREGATION OF HOMOLOGOUS CHROMOSOMES 477 



is concerned the manner of its origin is of minor importance. 

 The essential thing is that it exists, and is transmitted, not only 

 from cell generation to cell generation in the individual, but 

 occurs so definitely that one can predict the combinations that - 

 should occur in the population. Judging from the conditions 

 present in my material one would find all possible associations 

 if a reasonably large number of specimens were examined. 



Actual observation has shown the ratios of the telomitic to 

 the atelomitic dyads of chromosome number 1 to be 1 to 1. 

 In other words the variant, atelomitic homologue, occurs in 

 practically one-half of the .population. But we cannot gen- 

 eralize that this ratio holds, therefore, for all of the variants, 

 if we may so designate all atelomitic dyads. Tetrad number 

 three has only six atelomitic dyads out of a possible one hundred 

 and twenty-four in the sixty-two individuals represented (plates 

 2 to 9). It is impossible to calculate ratios for the occurrence 

 of any given combination in the general population unless one 

 knows in advance the frequency of occurrence of that particular 

 variation. 



It is hard to imagine a better example of persistent individ- 

 uality than that illustrated in figures 21a, 62/, 13a, plate 14 

 where a variation from the normal smooth rod form (fig. 13a), 

 such as the constriction of the dyads (fig. 21a), has been trans- 

 mitted, not only from cell to cell in one individual, but apparent- 

 ly on to the next generation, so that the union of a gamete carry- 

 ing such a chromosome with one bearing its normal homologue 

 has resulted in a zygote which shows both types clearly (fig. 62/). 

 This is the same principle found throughout this work where 

 no kind of heteromorphism (J-shaped tetrads and atelomitic 

 tetrads with unequal arms) has been found without homo- 

 morphic forms corresponding to both types of dyads occurring in 

 other individuals. 



There are but two other instances in all cytological literature 

 so far as I know where homologous chromosomes show morpho- 

 logical differences other than those of size. One of these is the 

 multiple of Mermeria (McClung '05). The other case is that 

 reported by Voi'nov ('14). It seems desirable to undertake a 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 2 



