CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 197 



The measurements represented in figure 35 are nearly as 

 reliable as those of the preceding cells. The amounts included 

 for very slight foreshortenings are indicated in figure 29. The 

 relative chromosome lengths form approximately the same 

 groups as those of the other cells, and the evidence for the 

 existence of pairs is strong. As contrasted with figures 33 and 34, 

 the chromosomes of pairs 1 and 2, when approximately corrected 

 for foreshortening, do not entirely meet the conditions of the 

 criteria, but their lengths and form strongly support the prob- 

 ability that they are homologues. The chromosomes of pairs 7, 

 8, and 10 differ somewhat in length. They do not appear fore- 

 shortened, and although possibly present there is no perceptible 

 stretching in them. These differences may be due to an un- 

 equalness of homologues as discussed later (p. 217). On the 

 other hand, the chromosomes of pairs 3 to 6, 9 and 11 to 13 are. 

 except as noted in figure 29, unforeshortened and of equal length, 

 they agree in form and present strong evidence for the exist- 

 ence of pairs. The greater part of the difference in length 

 between the homologues of pair 14 is due to stretching. 



The measurement of the chromosomes of the cell represented 

 in figures 30 and 36 are somewhat less favorable for measurement 

 than those of the preceding cells, because in addition to a 

 moderate amount of twisting there is slight foreshortening in 

 many of them. Although the lengths have been approximately 

 corrected for this foreshortening (figs. 30 and 36) the measure- 

 ments cannot be considered so accurate and reliable as those of 

 figures 33 and 34. The relative lengths of the pairs closely 

 parallels that of the preceding figures which results in a similar 

 distribution in the series. As contrasted with figures 33 and 34, 

 the chromosomes of pairs 1 and 2 fail to satisfy the criteria, 

 and this is apparently not due to errors in measurement. The 

 large difference of 5.6 mm. between the homologues of pair 7 

 recalls a similar difference in pair 9 of cell 33. Pairs 8 and 9 

 clearly satisfy the conditions of the criteria and the remainder 

 of the pairs duplicate the conditions in figures 33 and 34. 



The chromosomes of the cell represented by figures 24, 31, 

 and 37 are foreshortened in nearly every case and were measured 



