SPERMATOGENESIS IN THE ALBINO RAT 159 



The constitution of the first spermatocyte chromosomes 



As brought out in the early part of this paper, the constitution 

 or organization of the chromosomes of the white rat is to be 

 interpreted by regarding them primarily as simple, slightly 

 curved rods with terminal fiber attachment. By the synapsis 

 and longitudinal splitting of homologous chromosomes and by the 

 movement of the parts in the tetrad thus produced, the simple 

 and complex rings and the crosses which appear in the first 

 spermatocyte cells may be explained. Whether the pairing is by 

 telo- or parasynapsis, the fact seems to be that at least one end 

 of the diad is fused, as shown in figure 15. Since there are appar- 

 ently no unequal chromatids, it is likely that respective pairs of 

 homologous chromosomes are also equal. 



While evidence of the tetrad constitution in the diakmesis stage 

 of more of the chromosomes is desirable in order to complete, 

 without question, the morphological history of each member of 

 the complex, it is unnecessary for the large and intermediate- 

 sized ones, as their later stages show this constitution. Compara- 

 tive evidence from well-established data on chromosome organi- 

 zation is sufficient to fill the gap, since no shape is new and since 

 no peculiarity of organization appears. The field is open for 

 further investigation, to be sure, as the morphological evidence 

 must be the final determinant. Perhaps still more refined 

 methods of technique will give material that will fill this space. 



The work on the organization of mammalian chromosomes is 

 very slight and no one has carried it far. Duesberg ('08) shows 

 first spermatocyte figures which indicate the same kind of tetrad 

 formation which I have described, but he does not interpret 

 them as tetrads. In the first division it would appear from his 

 text-figure that he regards them as diads. He is clearly in error 

 in thinking that there is a transverse division of the chromosomes 

 after synapsis by which the various first spermatocyte shapes are 

 produced. Von Winiwarter's figures ('12) for man indicate 

 rings, both simple and compound. Figure 28 shows one directly 

 comparable to the rat chromosome which I have described as A. 

 But he does not carry the study on to the organization of the 

 , chromosomes. 



