STUDIES ON CHROMOSOMES. 233 



somes were not so long and the special, unpaired curved element 

 was frequently in evidence. While in some cases I have recorded 

 the occurrence of more than one curved element in individual 

 cells, these additional curved chromosomes were usually smaller 

 than the element in question and readily distinguished from it. 

 In the first hundred polar views of dividing cells showing any 

 understandable detail, recorded from one preparation of a ten- 

 day female chick, for instance, I find that 43 have a single un- 

 mistakable large curved element, 20 have a long element which is 

 probably the curved element with the curve turned directly 

 away from or toward the observer, and therefore out of per- 

 spective, 27 have a number of the chromosomes curved so that 

 it is impossible to pick out any special one as the particular 

 element in question, and 10 do not show what could positively 

 be identified as a special curved body, the doubt arising as to 

 whether what appeared to be curved element was not two 

 chromosomes with the ends overlapping. 



Photos 4 to 7 and Figs. 100 to 117 show characteristic appear- 

 ances of the cells of females as revealed by the photographic 

 camera, or the camera lucida. For the details regarding each 

 figure the reader is referred to the legend which accompanies it. 

 Fig. 115 represents a type found occasionally in which while an 

 actual curved element was not to be found, an individual chromo- 

 some much longer than its mates was to be seen and is probably 

 to be interpreted as the special element in question. Not 

 infrequently it held the hsematoxylin stain much less tenaciously 

 than did the ordinary chromosomes, becoming yellowish brown 

 in color, while they remained black. Fig. no shows this lighter 

 staining element as unmistakably curved. Photos 6 and 7 are 

 side views of equatorial plate stages. Each shows a special 

 elongated chromosome at one edge of the chromosomal plate. 

 While these elements do not appear in the photograph to be 

 curved as a matter of fact a slight shift of focus of the microscope 

 reveals a decided curvature in each. Although in many cases 

 the flat surface of the curved element was turned at right angles 

 to the long axis of the spindle (Figs. 107, no), not infrequently 

 it lay parallel to the latter as in Fig. 108 or even at an acute 

 angle. 



