250 CHARLES W. METZ 



in pairs through side by side approximation. Upon this basis 

 he decided that the entire hypothesis of chromosome pairing 

 is a delusion. His attitude toward this matter, however, is 

 so obviously biased as to discount very materially his whole 

 argument. Dealing as he does with a chromosome group com- 

 posed of large, numerous and almost uniform members it is 

 little wonder that he finds no conspicuous evidence of their being 

 differentiated into pairs. The wonder is that he attempts to 

 draw conclusions of any final nature regarding this problem 

 from material so evidently unsuited for its solution. The only 

 answer to be given to Meves argument is that it does not accord 

 with the facts as presented by organisms in which the chromo- 

 somes are sufficiently differentiated to be susceptible of analysis. 

 The conclusions of Meves on this question have been directly 

 controverted by von Baehr, Montgomery, Miiller ('12), Lunde- 

 gardh ('13) and others. 



The criticism of Dehorne and his adherents is in the nature 

 of an alternate theory, based upon the conclusion that all chromo- 

 somes are constantly dual or quadruple in form. Upon this 

 basis 'pairs' of chromosomes are very readily explained as simply 

 being halves of single chromosomes derived from a precocious 

 split. If the two members are themselves split, then the single 

 chromosome is represented by a quadruple element or tetrad. 

 According to this theory each univalent, metaphase chromosome 

 is represented by four parallel elements or two dyads. During 

 anaphase these dyads separate from one another (passing to 

 opposite poles) and then immediately split again to re-form the 

 tetrad. Thus a quadruple structure is maintained throughout 

 the greater part of any cell generation. 



Such a theory, if true, would afford a very simple explanation 

 of 'pairing'; but unfortunately it cannot be reconciled with 

 the facts. In the first place Dehorne's evidence is directly 

 contradicted by the actual history of the chromosomes as re- 

 examined by Gregoire and Muckermann; and in addition, as 

 pointed out by these authors and by von Schustow ('13) and 

 von Baehr ('11) it takes no account of the relation between 

 haploid and diploid groups or of the evidence furnished by the 



