170 
CHARLES L. PARMENTER 
INTRODUCTION 
It is believed (McClung, ’17, pp. 536-38) that the chromatin 
of an organism is, for the most part at least, the idioplasm, and 
consists of a definite linearly arranged series of differentiated 
materials which is perpetuated from generation to generation. 
The chromosomes which are essentially constant in number in 
an individual are thought to constitute the visible mechanism 
for this perpetuation. This conception is known as the theory 
of the individuality of the chromosomes, which is quite generally 
accepted by all who have an intimate acquaintance with chro¬ 
mosome behavior. However, there are a few not so acquainted 
who strenuously oppose the theory. 
Among these is Della Valle (’09, ’ll, ’12), who presents some 
data and a large amount of discussion in an effort to disprove 
this theory upon the claim that the chromosome number in an 
individual is not constant, but is simply the quotient of the 
quantity of chromatin divided by the average size of the chro¬ 
mosomes. This removes from them any constancy of organiza¬ 
tion and contradicts the above theory. These observations have 
been cited by other opponents of the theory as cytological 
evidence in favor of their contentions. Della Valle’s conclusions 
are based upon observations made upon dividing cells of the 
peritoneum and blood-cells of Salamandra maculosa, together 
with a large amount of data taken from the observations of 
others. 
Meves (’ll) and Della Valle (’12) further oppose the theory 
upon the basis of linear measurements made upon the spermat- 
ogonial and somatic chromosomes of Salamandra maculosa in 
denying Montgomery’s (’01) and Sutton’s (’02) claim that the 
chromosomes occur in pairs whose homologues are of equal 
length, and that approximately constant size relations among 
chromosomes are maintained from one cell generation to 
another. 
In the spring of 1916 I was fortunate in obtaining peritoneal 
and other somatic tissues of Ambystoma tigrinum. This made 
it possible to repeat Della Valle’s observations upon the somatic 
