CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 203 
have made extended and careful studies of the germinal and 
somatic mitoses of the same species mention no variation in 
chromosome number. Furthermore, Meves (’ll), who attacks 
the theory of individuality, fails to substantiate Della Valle’s 
observations, and it is not at all likely that he would have failed 
to mention any variation observed. He appears to believe (p. 
296) that the number is constant. However, Heidenhain (’07, 
p. 176, figs. 80 and 81) shows a polar view T of a late prophase 
and a lateral view of a metaphase with twenty-six and twenty- 
two chromosomes, respectively, and states that such irregu¬ 
larities occasionally occur. An occasional variation is not sur¬ 
prising, but variations as numerous as Della Valle claims to be 
present are unusual. Flemming (’90, p. 78) states that he 
observes in the lungs of Salamandra maculosa numerous atypical 
rqitoses with very short chromosomes. He gives no further 
discussion and no figures to indicate what kind of cells they are 
nor whether they are normal. In the ten cells of the lung of 
Ambystoma tigrinum (table, p. 177) there were no variations in 
chromosome number, and with the exception shown in figure 26 
I observed no abnormalities. Della Valle’s (’ll) figures of blood 
cells in Salamandra maculosa, which he claims show an extreme 
variation in chromosome number, appear very much like cells 
undergoing disintegration. 
To the above evidence of the questionableness of Della Valle’s 
results may be added the results of the sixty-six counts in Amby¬ 
stoma tigrinum showing no variation in number. The important 
fact that these counts were made with extreme care (p. 177) in 
the somatic cells of the same and other tissues of a closely related 
species, and made in uncut membranes (which Della Valle 
emphasizes as important for accurate counts), further strengthens 
the already strong probability that his number determinations 
are incorrect. 
There are certain characteristics in his figures that also indicate 
that his drawings are none too accurate. He notices that the 
chromosomes are twisted, but he does not show what constitutes 
the twist. That the peritoneal chromosomes of Salamandra 
maculosa are each composed of two separate chromatids twisted 
