66 ALICE M. BORING AND RAYMOND PEARL 



the microscope is focused on the right pole instead of the left, 

 arms appear which might be considered the mates of the other 

 two arms of the left pole. 



Figure 66 is also a first spermatocyte anaphase. The three 

 or four-parted body toward the upper pole might be an X-chro- 

 mosome, but the chromosomes are so loosely grouped here, and 

 the separate body is so close to the pole that such an interpreta- 

 tion has no particular probability in its favor. 



Figure 22 a is a second spermatocyte equatorial plate. The 

 body to the left may be one rod-shaped X-chromosome, or two 

 round ones, or not an X-chromosome at all. 



Figure 81 is a second spermatocyte metaphase spindle. The 

 part projecting toward the lower pole might be a univalent X- 

 chromosome, or one part of a large bivalent dividing. 



Figure 83 is a second spermatocyte anaphase. The three- 

 parted body at the lower pole may be an X-chromosome, or it 

 may be the mate to the projecting mass at the upper pole. The 

 small round chromosome at the lower pole may be a second X- 

 chromosome, or it may be one of the ordinary chromosomes with 

 its mate fused in the mass at the upper pole. 



Similar varying interpretations might be given for most of the 

 figures. There would then appear to be abundant justification 

 for the statement that there is no valid evidence of the existence 

 of an X-chromosome in the Barred Rock male, on the following 

 grounds : 



a. The small percentage of cells containing any element which, 

 on the most liberal interpretation, could be regarded even as a 

 possible X-chromosome. 



6. The inconstancy of the shape, size and number of these 

 possible X-chromosomes. 



c. The fact that many (not to say most) of them would never 

 be considered to be sufficiently proved as X-chromosomes if this 

 were insect material. 



The 11.82 per cent of first spermatocytes and the 3.06 per 

 cent of second spermatocytes classified in the table as 'with X,* 

 however, demand further attention. The projecting arms and 

 those lying in close juxtaposition to the equatorial plate have 



