SPERMATOGENESIS IN THE ALBINO RAT , 143 



of A, which is usually retarded in its differentiation. It is pos- 

 sible that the obscure chromosome is A in an abnormal condition, 

 but this hypothesis is only suggested. 



No other cell found showed its chromosomes clearly enough 

 for an accurate identification of more than thirteen out of the 

 full number of nineteen present. 



The high percentage of rings is always manifest. The inter- 

 mediate-sized rings are so nearly of the same size that their 

 individual measurement is very questionable. It would prob- 

 ably be possible to differentiate them were they all to lie per- 

 fectly flat, a position which, unfortunately for this purpose, they 

 do not assume. The. exact size relation is not shown in figure 27, 

 since some are inclined or curved to the plane of drawing. B 

 is actually larger than it appears in the figure. A is always con- 

 siderably larger than B (perhaps one should say longer), and 

 probably for that reason lags behind the others in its condensa- 

 tion, a circumstance which tends to over-emphasize its actual 

 size when measured in quantity of chromatin. 



The chromosomes marked A, B, C, and D in the various figures 

 are recognizable in different stages. B and C resemble each other 

 after early prophase. Chromosome C may be early identified 

 by its strongly elliptical outline and open ends, as in figure 27. 

 Whether it originates as a double ring like B is still a question, as 

 I have not seen two large double rings in any cell in which A is 

 present in its triple-ring form. Chromosome D is early identified 

 by its widespread lugs at one side and closed-ring formation at 

 the other, as shown in figure 27. This chromosome is trouble- 

 some in polar views of metaphase plates, as may be judged from 

 its form and from its appearance in figures 18 and 19. Chromo- 

 some C is marked doubtful in figure 19. It is either a cross or a 

 ring with widespread lugs, the parts in such position as to ob- 

 scure the opening. If a ring, it is identifiable as chromosome C 

 by its size. 



The identity in late anaphase of chromosomes A and B is of 

 course doubtful, as they are both large. Figures 39 to 42 would 

 do as well for A as for B. The size is the only distinguishing 

 character in these stages. Likewise C and D in similar stages, 



