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CHARLES L. PARMENTER 
just as difficult to demonstrate the absence of pairs. It seems 
to me that the evidence in the Dipteran somatic complexes, 
where the members of a pair lie parallel and adjacent to one 
another, together with the already large and well-supported 
evidence of pairs in the various generations of the germ cells 
throw the balance greatly in favor of the presence of homologues. 
DISCUSSION 
A. Introductory statement 
The foregoing observations upon the constancy of chromosome 
number and the existence of pairs in the somatic chromosome 
complexes have their chief importance in their relation to the 
Roux-Weismann hypothesis that the chromatin is the idioplasm, 
which is differentially organized and linearly arranged, and 
that this organization is perpetuated. This hypothesis received 
important support from the theory of the individuality of the 
chromosomes as set forth by Van Beneden (’83) and strongly 
maintained by Rabl (’85), Boveri (’88, ’02), and numerous other 
more recent investigators. The morphological evidence ac¬ 
cepted as supporting this proposition is an essential constancy 
of number, size, form, and behavior. 
Since McClung (’17) has so recently thoroughly considered 
the theory of individuality, this discussion is confined to the 
particular phases of the supporting evidence which are directly 
related to the observations made upon this material. These 
phases are essential constancy of number, of size, and of form. 
B. Constancy of chromosome number 
Della Valle has strongly attacked this theory on the basis of 
inconstancy of chromosome number. He arrives at the con¬ 
clusion (’09, p. 120 ff.) that the number of the chromosomes is 
the quotient of the quantity of the chromatin divided by the 
average size of the chromosomes; that their size is variable 
according to the nature of the elements and the conditions in 
which they are found, and (’ll, p. 188) that the size and number 
