STUDIES ON CHROMOSOMES. 23! 



details were to be seen in the dividing cells of the nephridial 

 tubules. The chromosomes of this tissue tend less to stick to- 

 gether than do those of the testis and they also stain more 

 sharply. One obvious reason for the greater clearness of equa- 

 torial plate stages in such nephridial cells is due to the fact 

 that in dividing to lengthen the tubules, the chromosomes lie 

 at the equator of a spindle which has its longitudinal axis across 

 the shorter diameter of the cell (Fig. 104). This shortening of 

 the spindle produces a proportionally greater equatorial spread 

 with the result that the chromosomes are spaced further apart. 

 The legends accompanying the respective photos and figures 

 state whether the picture in question is of a somatic or of a 

 germ cell. 



Photos i to 3 and Figs. 70 to 99 show representative conditions 

 in various somatic and spermatogonial cells. Most of them 

 speak for themselves. In such figures as 86, 87 and 98 the pairs 

 of special elements appear as of inordinate size. This is due in 

 part to their actually greater size but also to the fact that the 

 ends of most of the other chromosomes have been cut away in 

 the preceding and following sections. 



Photo 3 is of a spermatogonium of an adult cock. While the 

 ordinary chromosomes were clumped so that little detail could 

 be determined beyond the fact that there were no long curved 

 elements among them, the two special elements lay well to one 

 side and were particularly easy to identify. As already mentioned 

 the spermatogonia of adult fowls were much less satisfactory to 

 study in detail than were those of embryonic chicks. However, 

 various other spermatogonia in adults, showing the two curved 

 chromosomes, were found as were also a number in the guinea- 

 fowl, and hosts of them were discovered with two special pro- 

 jecting elements which one suspects of being the same curved 

 elements as are visible in spermatogonia and somatic cells when 

 conditions can be clearly seen, but concerning which one is not 

 absolutely sure. In any event such conditions do not negate 

 the evidence found in the more favorable cells. 



The relative positions of the two elements usually in evidence 

 were, for example, approximately those indicated in such cells as 

 photos i and 2 and Figs. 71, 72 and 76. That is, when seen in 



