56 CHARLES W. METZ 



figures closely resemble those of haploid groups. Apparently 

 this takes place especially in early prophase (fig. 24), but a second 

 conjugation may occur during metaphase, just a short time before 

 division (figs. 9, 15, 16). Whether in the first case conjugation 

 takes place in anaphase and continues into the succeeding pro- 

 phase has not been ascertained. This interesting question is 

 being given special study at the present time, with a view to de- 

 termining the exact nature and extent of the conjugation. In the 

 second, or metaphase conjugation, at least, it is worthy of note 

 that the union is unquestionably a side-by-side, or parasynaptic 

 one. 



It need hardly be urged, in the face of such evidence as this, that 

 an actual pairing of chromosomes may take place in the diploid 

 nuclei outside of the sphere of reduction. True, there is little 

 evidence, in most organisms, of such a side-by-side association of 

 chromosomes to form pairs. But the fact that it occurs so strik- 

 ingly in some forms adds great weight to the conclusion (based on 

 size relations and other evidence), that such pairs are present in 

 all, even when the members are not obviously associated. If 

 anyone still doubts the reality of pairing of homologous chromo- 

 somes, I should recommend to him a study of the Diptera. 



In conclusion, I wish to express my appreciation of the kindly 

 assistance and advice of Professors E. B. Wilson and T. H. Mor- 

 gan of this laboratory. And I wish to thank Dr. C. B. Daven- 

 port for the many courtesies extended to me during my stay at 

 Cold Spring Harbor. 



Addendum. Since this paper went to the publisher, further 

 study of D. funebris (Type III) has revealed the presence of a 

 minute pair of w-chromosomes in at least some specimens of 

 this species. Apparently either the size of the m-chromosomes 

 is variable in D. funebris, or else these chromosomes are absent 

 in some specimens and present in others. 



