674 C. E. McCLUNG 



plane of the spindle axis. The extremes of such a process are 

 shown by two chromosomes lying side by side in one cell as repre- 

 sented in figure 64 e. 



While for the sake of convenience in analysis the conditions 

 of the prophase have been considered separately from those of 

 the metaphase, the facts indicate that the changes in form are 

 continuous and may proceed in varying degrees in different 

 chromosomes during any one phase. For the same reasons the 

 different chromatid movements have been reduced to types, but 

 it is observed that they are rarely simple and that they occur in 

 different combinations so that in most cases, in any one chromo- 

 some, it is necessary to resolve the changes into their components. 

 When this is done for the metaphase chromosomes it is found 

 that in general there is more or less bending or flexure in the 

 plane of the longitudinal division combined with varying degrees 

 of extension of homologous chromatids side to side at right angles 

 to this. These two movements are sufficient to account for. by 

 far the greater number of metaphase chromosome forms and 

 exclude the possibility of the occurrence of fundamentally differ- 

 ent chromatid arrangements. 



c. Relations of chromosomes to archoplasmic fibers 



(1) As a part of the relations in the metaphase there must be 

 considered those between the chromosomes and the archoplasmic 

 fibers. It is not pertinent, in Orthopteran cells, to speak of the 

 fibers attaching to the chromosomes as 'mantle fibers' for the 

 reason that the spindle encloses the area occupied by the chromo- 

 somes and of itself constitutes a mantle (fig. 129). Nevertheless 

 there are definite fibers attaching to the chromosomes and the re- 

 lation thus estabUshed is most precise and constant. With but few 

 exceptions fiber attachment is at the center of the rod or V-shaped 

 chromosomes or, in the various modifications of this simple form, 

 at the corresponding place, which is the point of fusion between 

 homologous spennatogonial chromosomes. Directly related to 

 the foraa of the tetrad and to the character of its movements is 

 this fiber attachment, for it fixes the position of the chromosome 



