316 



C. E. MCCLUNG. 



chromosome in the multiple element. Whether the tetrad that is 

 added to the multiple chromosome attaches to the accessory end 

 of the trivalent element of the prophase, or to the other extremity, 

 I have not made out with certainty. The final result of the 

 divisions would not be different in either case. 



Upon the separation of the chromosomes in the metaphase 

 the multiple chromosome is divided so that to one pole there 

 goes a trivalent element and to the other a bivalent one, the dif- 

 ference in valence being due to the presence of the accessory 

 chromosome in one daughter cell. There occurs here an entirely 

 unique separation of chromosomes, for by means of it entire 



FIG. 12. Metaphase of first spermatocyte in Mermiria showing the decad in pro- 

 file and a number of the tetrads. Observe that the fibers attach at the point of con- 

 tact between two chromosomes and not at the free ends of the chromosomes. A very 

 large part of the cytoplasm is organized into the spindle and the remainder of it is 

 measurably polarized. 



tetrads pass into the second spermatocyte s. If these bivalent 

 structures are always produced by the fusion of paternal and 

 maternal chromsomes, then in this case both such pass into one 

 cell. The alternative possibility that they are not homologous 

 chromosomes will be discussed in the latter part of this paper. 

 When the second spermatocyte mitotic figure is formed it is 

 seen that the accessory has separated from the dyad with which 



