216 CHARLES L. PARMENTER 



given in his tables and curves, between the measured lengths of 

 the chromosomes and the computed lengths that would be 

 expected if the chromosomes were such a series of variants. 



I believe Delia Valle's conclusions are incorrect for the fol- 

 owing reasons: 1) He fails to demonstrate the presence of 

 chromosome pairs because, a) as discussed on page 201, his chro- 

 mosome enumerations are probably incorrect and therefore his 

 measurements do not represent the actual conditions; b) his 

 measurements probably contain numerous errors of varying 

 magnitude due to foreshortening (as well as to errors arising 

 from measurements upon single drawings) even though he chose 

 for measurements strongly flattened cells (p. 126); c) the dif- 

 ferences in the lengths of these chromosomes are so small and 

 the errors so great that it is impossible either to demonstrate or 

 to deny a presence of pairs, 2) Failure to find a constant 

 grouping among the chromosomes would result from the causes 

 given in (a) and (b). 3) His interpretation that the chromosome 

 lengths are controlled by the law of fluctuating variations is 

 untenable because, even if his measurements were reliable and 

 whether pairs do or do not exist, the differences in length between 

 the chromosomes of Salamandra maculosa are so small that the 

 degree of correspondence between their measured lengths and the 

 calculated lengths of a series of variants, corresponding respec- 

 tively to each of these chromosomes, would be fully as close as 

 those which he presents in his tables and curves containing 

 numerous and large differences. 



3. Results in Ambystoma tigrinum. The chromosomes of Am- 

 bystoma tigrinum, fortunately, are more favorable subjects for 

 measurements than those of Salamandra maculosa, because the 

 relative differences in length between many pairs is so large 

 that certain pairs and certain groups of pairs stand out con- 

 spicuously. The evidence presented in figures 33 and 34 is free 

 from all errors of measurement except those due to twisting of 

 the chromatids and to minute foreshortenings at non-critical 

 points in the series. These errors have been approximately 

 eliminated (p. 188) and do not seriously disturb the critical evi- 

 dence of the chromosome pairs which are much shorter or longer 



