670 C. E. McCLUNG 



larity in direction and contour of the parts. Nevertheless the 

 various forms of this late period may be traced back by gradual 

 steps into the earliest stages of the prophase where all the chroma- 

 tin elements are in the form of very elongated, delicate threads 

 such as are shown in figures 99, 101 and 105. These stages are 

 best seen in smear preparations in which the nuclear elements 

 are more isolated and where their parts are more distinct. There 

 can be no doubt of the composition and movements of these 

 tetrads and the only uncertainty relates to the early stages where, 

 for a time, it is impossible to trace the individual chromatids. 

 Whether telosynapsis alone, or parasynapsis in connection with it, 

 is the history of chromosome association has not yet been defi- 

 nitely determined, but however this may be, it is certain that the 

 four parts of each chromosome are derived by the longitudinal 

 splitting of two homologous spermatogonial chromosomes. 



CHROMOSOMES OF FIRST SPERMATOCYTE METAPHASE 



a. Identification of first spermatocyte metaphase chromosomes with 

 those of the prophase 



At the end of the prophase the forms of the chromosomes have 

 been established and, upon the dissolution of the karyotheca, they 

 lose their granular character and become homogeneous. Aside 

 from this they suffer no important change and all the forms seen 

 in the prophase, with the exception of those resulting from wide 

 separation of the chromatids at the middle of the tetrad, may be 

 traced into the equatorial plate. Since however there have been 

 extensive and continued movements of the chromatids with rela- 

 tion to each other, it is only reasonable to expect their continuance 

 during the metaphase, and this, in fact, occurs. Regarding 

 however the late prophase and early metaphase it may be stated 

 that the chromosome forms of the early condition may be traced 

 directly into the later, and what changes there are may be ascribed 

 to a continuation of processes already in operation. It is essen- 

 tial to note this, for by some the bipolar condition of the cell is 

 considered to inaugurate entirely new conditions and the separa- 



