240 MICHAEL F. GUYER. 



the fact that the cell is in process of division. To determine 

 detail regarding a particular chromosome, one naturally has to 

 ignore such preparations and choose only those cells which 

 either show evidence for or against the point at issue. There 

 is always a residue of cells which must fall in the neutral zone of 

 non-significance, and this residue of course becomes increasingly 

 great when one is dealing with inherently unfavorable material, 

 as the germ-cells of the rooster undeniably are. Even in as 

 classical and clear cut an object as Ascaris with its small number 

 of chromosomes, I find that a large percentage of the cells show- 

 ing chromosomes give no clear cut evidence of the conditions 

 which we universally teach as characteristic of Ascaris. On the 

 other hand they do not negate these teachings. 



Regarding the X-like element of the male fowl I found that it 

 exists in great abundance. Up to date I have in my notes 963 

 unequivocal cases recorded in primary spermatocytes, to say 

 nothing of many other cases I have seen but not specifically 

 noted down. In the field under the microscope from which 

 such photos as 9 and 34 have been taken, under slightly lower 

 power some 3 to 5 other division figures each showing such a 

 curved element may be seen. The element in question when 

 seen from the side is always in the form of a curved rod, usually 

 thick and plump looking, though occasionally more slender 

 and proportionately longer. Photo 8 is a good clear-cut example 

 of how it appears in a favorable preparation. Inasmuch as it 

 may lie in almost any conceivable position with reference to 

 the pole of the spindle, or the point of view of the observer, 

 obviously the majority of views of it will be at some other angle 

 than that depicted in photo 8 and correspondingly difficult to 

 represent by photography. Indeed, for every one to be found 

 in a suitable position to photograph, many could be positively 

 identified as the same element, but lying in such a plane that some 

 shift of the fine adjustment of the microscope was necessary to 

 see the w T hole chromosome. Often tangentially lying elements 

 or those with the curved surface turned directly toward the 

 observer require careful focusing to determine the exact shape 

 and dimensions of the object. 



Photos 12, 14, 23 and 27, when examined under the microscope 



