230 MICHAEL F. GUYER. 



were so massed as to prevent an accurate enumeration beyond 

 observing that other curved ones comparable to the pair in 

 question did not occur. In general, the other chromosomes were 

 smaller and usually appeared as straight, very short or moderately 

 long rods (photo I, Fig. 72). In some instances a number of 

 chromosomes appeared curved and a particular pair could not 

 be picked out with certainty though such cases were relatively 

 rare (not over 15 per cent, of the cases) when compared with 

 the number in which the typical pair were observable. Many of 

 the cases which at first seemed to be exceptions were, upon 

 careful scrutiny, resolvable into instances in which the ends of 

 two chromosomes swung together, forming a V which at first 

 sight had been mistaken for a single curved element. Fig. 76 

 shows such an instance; the pair at the right might easily be 

 mistaken for a single chromosome. This mistake is particularly 

 easy to make since the real curved elements frequently show an 

 abrupt bend rather than a long even curve. It is also an error 

 easily fallen into with material stained in iron-hsematoxylin 

 unless the preparation is strongly decolorized. 



As is likely to be true in much cytological material in general, 

 many cells, although in stages of division, were so affected by 

 the reagents or lay in such a position as to render them worthless 

 for accurate observation. These have necessarily been dis- 

 regarded as it was wholly impossible to affirm that they either 

 bore out or negated the observations made upon more favorable 

 material. Where figures or photos have been made from sec- 

 tions showing only a part of a cell or a part of the chromosomes, 

 as was frequently the case, the preceding and following sections 

 have been carefully inspected to insure as far as possible that the 

 condition intended to be conveyed by the figure is not a mis- 

 leading one. 



Confusion is most likely to arise in late prophase, when the 

 chromosomes have arrived at their rod-like form but have not 

 yet settled down to their final size and position before division. 

 Then, all may show some degree of curvature and one cannot 

 identify with certainty the special pair. 



While many observations were made upon the dividing cells of 

 the embryonic testis, as a matter of fact the most satisfactory 



