204 
CHARLES L. PARMENTER 
about one another is plainly evident in Meves’ (’ll) figures 11 
to 15 which show each chromosome to be of variable width. 
These figures are exactly comparable to my figures 1 to 8, and 9 
to 23 which demonstrate that this variation in width is due to 
the twisting of the chromatids. Della Valle represents each 
chromosome to be of uniform width excepting an occasional 
split in the end of some chromosomes. If he does not see chro¬ 
matids in any of the chromosomes which he has drawn, either 
his observations, his technique, or both are faulty. Further¬ 
more, the above evidence together with his attitude make it 
uncertain whether his preparations were as clear or the chromo¬ 
somes as distinctly separated from one another as his drawings 
indicate. 
Finally, Della Valle’s above demonstrated attitude, the ab¬ 
sence of confirmatory evidence for his contentions, his question¬ 
able ability as an observer as indicated by his drawings, and the 
results of critical counts in Ambystoma tigrinum, all support 
the view that his observations and conclusions are incorrect. 
But upon the assumption that they may be partially correct, 
there are some possible explanations for the presence of variation 
in the peritoneum of Salamandra maculosa. 1) One or more 
chromosomes of a complex easily could have been disturbed, as 
is evident from my figures 22 and 24 to 26. This could account 
for number deficiencies and perhaps also for excesses. 2) 
Champi (T3, p. 181) claims that chromosome number can vary 
by fragmentation under the influence of certain external stimuli. 
Della Valle (’09, p. 86) says the number of mitoses can be in¬ 
creased by keeping the larvae covered with a blue glass. If 
Della Valle did this, and if such a stimulus could produce frag¬ 
mentation, a bare possibility is offered for a disturbance of 
chromosome number. 3) There is also a slight possibility that 
the larvae had been kept in captivity and might in consequence 
have been sufficiently pathological to produce abnormal mitoses. 
4) In an investigation on certain Orthoptera now in progress in 
this laboratory, Mr. Carroll observes that in three individuals 
some of the few dividing spermatogonial cells contain, in ad¬ 
dition to the normal number of twenty-three, one, and some two 
