Oll the Dimcgalous Sperm and Cliromosomal Vaiiatioii of Euscliistus, etc. 139 
of chromosoines inay be due to better conditions of iiourishment, and 
variability in numbcr to externa! conditions. The variability of their 
size in a particular mitosis corresponds to partial variability, and that of 
them in two different mitoses to individual variability. The diverse 
size of the chromosoines is the expression of the association of a greater 
or less number of chromatin elements, of a practically infinite number, 
in groups variably numerous according as the conditions are favorable 
in which they segregate. The variability in number generaUy foUows the 
law of Chance; but some cases may be considered true mutations (as 
change in number in the body cells of Ascaris). In somatic cells the varia- 
bility is probably more than in the germ cells. 
Della Valle’s only new observations that he brings in favor of his 
view are counts of the number of chroniosomes in 40 mitoses of the peri- 
toneal mcsothelium of larvae (exact stage not stated) of Salamandra ma- 
culosa. He chose this object on account of the large size and extreme 
flatness of the cells, which could be studied without the section method. 
These counts resulted as follows: 
Xo. of chromosoines 19 20 21 22 23 24 25 26 27 
Xo. of mitoses 10116 16 12 21 
He considers that these counts positively demonstrate a numerical varia- 
bility of the chroniosomes in ceUs of a honiogenous groiip. Since they 
compose the whole of his new evidence they shoiild be faultless, but I think 
we may make the following objections to them: 1. The chromosoines 
counted are long, siniious ribbons, that overlap and interlace, the most 
difficult kiiid to coiiiit with accuracy. 2. He included in the counts some 
cells in prophases, where one cannot be certain that all the chromosoines 
liave fully separated. 3. The total number of the chromosomes is so large, 
about 24, that the chance of error in cnumeration is great. It is but fair 
to conclude that while his technique was excellent, his choice of material 
was bad, consequently a degree of scepticism might well be maintained 
towards his results. 
Then Della Valle brings together froiii the scattered literatiire all 
cases implying that the number of chroniosomes is variable in ceUs of the 
same generation from the same species. He has done a great Service in 
caUing attention to these cases in plant as well as animal cells. AVhen 
one examines the long lists of them one might well believe at first sight 
that they furnish a formidable array of evidence for his conclusions. 
But in the fhst place he holds that constancy in number is essential for the 
theory of chromosomal individuality, and if there is no such constancy 
