226 Proceedings of Indiana Academy of Science 



becomes, is seen occasionally to break up into a large bivalent and 

 a small univalent chromosome (figs. 11, 12). The separation of the 

 small univalent from large bivalent seems to take place in only a 

 small percentage of the dividing cells while a condition similar to 

 figure 10 is very often found. 



With the spermatogonial count of 25 it would be expected that the 

 metaphase counts of the first spermatocyte division would show 13, but 

 such was not the case except in a small percentage of the counts. By 

 counting only clear metaphase plates it was found that 92 per cent 

 showed 12 chromosomes (figs. 13, 14). The study of the side views 

 of the metaphase division showed clearly that the univalent chromosome 

 did not lie in a different plane from that of the bivalent chromosomes 

 nor did it pass to the pole before the division of the bivalents as has 

 been described in several instances. In a very few of the cells examined 

 it was found that a small univalent chromosome could be seen in the 



Fins. .")-12. (5. (5 and 7), Gi-ovvth pciiod showing dark staininvt bodies; (8 and 9), 

 prophase, dark staininjj body becoming unequal pair; (10), later prophase showinK un- 

 equal pair; (11 and \'Z) , small univalent separatin:.; from bivalent chromosome. 



side views • (figs. 17, 18). This accounts i'or the small percentage of 

 13 counts (figs. 1.5, 16). 



The metaphase counts of the second spermatocyte division showed 

 no such irregularity in chromosome behavior as that found in the first 

 spermatocyte division. Of the 513 counts made of this division 280 

 showed 12 (figs. 32, 33) and 233 showed 13 (figs. 34, 35). A study of 

 the side views of the division showed that all the chromosomes divided 

 normally. 



From the above facts it appears that the real problem here would 

 be to account for the disappearance of the univalent chromosome that 

 was present in the spermatogonial metaphase and its reappearance in 

 the second spermatocyte division. The second spermatocyte counts 

 .showed nearly equal numbers of twelve and thirteen chromosomes. This 

 is just what would be expected when the spermatogonial number is 25. 



In the growth period and early prophase one of the dark staining 

 bodies was seen to give rise to an unccjual pair of chromosomes. This 



