SPERMATOGENESIS IN THE ALBINO RAT 137 



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The Spermatogonial chromosomes 



Figure 16 is drawn from a cell showing 37 chromosomes in 

 metaphase. They are all rod-shaped, slightly curved, and of 

 about equal diameters. I have not been able to differentiate 

 an accessory in the spermatogonial complexes, although many 

 cells have been examined with this in mind. The cell figured 

 is taken to be typical with respect to number. Additional 

 evidence for this number consists of another cell divided 

 between two sections which shows clearly 31 chromosomes 

 in one section and 8 in the next; and of a few more cells 

 which show in each case clearly /30 plus some more which are too 

 intermingled for accurate counting; also of a cell in the cere- 

 bellum of a male rat which shows clearly 37 chromosomes. In 

 no case has a count yielded less than 30 plus some indistinct ones, 

 neither has there been positive evidence to indicate a greater 

 number than 37. The haploid number strengthens the accept- 

 ance of 37 as the basal number, as there is abundant evidence for 

 fixing this at 19 including the single accessory. The small size 

 and the strong tendency of the chromosomes to lie in more than 

 one plane closely overlapping each other are two conditions which 

 have proved serious obstacles to accurate enumeration. 



As seen in the figure, the chromosomes differ widely in lengths 

 — 14 long, 13 medium, and 10 short. The dividing line between 

 the second and third groups is less distinct than between the 

 second and first. The chromosomes marked A are the longest 

 pair and can be followed through other stages. The difference 

 in size between the second and third largest pairs is not so great, 

 and consequently they are difficult to determine accurately. 

 All are more or less curved. In the young testis they are longer, 

 less dense, and more scattered than in the adult. Many adult 

 cells were studied, but not one was found which was satisfactory 

 for an accurate count. I have not attempted counts in the late 

 prophase stages because the chromosomes are seldom in such 

 position as not to obscure each other in some degree, although it 

 may be possible to use this stage for number determination. 



Figure 17 shows that division is normal, i.e., longitudinal. 

 The fiber attachment is terminal. 



