SPERMATOGENESIS OF THE CHICKEN 



61 



from the mass, as in figures 1 and 13. On this basis, 1003 cells 

 were grouped into six classes with X and six classes without X. 

 The six classes are (1) first spermatocyte, equatorial plate; (2) 

 first spermatoc^^te, metaphase spindle; (3) first spermatocA'te, 

 anaphase; (4) second spermatocyte, equatorial plate; (5) second 

 spermatocyte, metaphase spindle; and (6) second spermatocyte, 

 anaphase. The results are given in table 1. These figures 

 plainly show that the so-called A"-chromosome is an exception 

 rather than a rule. Eighty-one cells with X out of 1003, that is 

 8.07 per cent, is obviously too few to justify a generalization as 

 to the specific character of the element, even with all the possible 

 chances of its escaping notice. This table also gives numerical 

 expression to the difficulty before mentioned, that X appears in 



TABLE 1 



both first and second spermatocyte divisions. If this were a 

 form where X passed undivided to one pole in the first spermato- 

 cyte division, 11.82 per cent cells showing it in the first spermato- 

 cyte would be too few, and 3.06 per cent in the second spermato- 

 cyte would be too many. If on the other hand this were a case 

 where the odd chromosome failed to divide in the second spermato- 

 cyte division, 11.82 per cent cells showing it in the first spermato- 

 cyte division would be too many, and 3.06 per cent too few. So 

 the actual facts will fit neither case. And we see now whj^ the 

 situation found by Edwards in Ascaris where the X-chromosome 

 divides sometimes in the first spermatocyte division and some- 

 times in the second, will not answer here: 8.07 per cent is still 

 not enough cells with X, even allowing for this possibility of 

 variation in behavior. 



