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 Della 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 
