On the Dimegalous Sperm and Chromosomal Variation of Euschistus, etc. 143 
without weight if the chromosoines be enzyme inasses as I have argiied 
iii the present paper. Then the cases of Ascaris, Helix and Strongylo- 
centrotus where the number of chromosoines is either n or 2n are ciirious, 
but they do not speak for a condition of flnctuating Variation, and may 
be more readily explained as an additional division of all the .elements. 
On the whole, accordingly, Della Valles view of the lability of the 
chromatin cannot be said to be substantiated by him, for his new evidence 
is open to criticism on accoimt of his material being unfavorable ; his thesis 
that constancy in number of chromosomes is essential for the theory of 
the indmduality of the chromosomes is not correct; many of the cases 
he adduces from the literature are not admissible because they are more 
readily explained in other ways; and he evades mucli of the evidence 
that speaks most strongly for the idea of the continuity of the chromo- 
somes. And it is fair to say, that if it be offen difficult to establish con- 
stancy in cliromosomal behavior, it becomes niuch more difficult to prove 
fluctuation. All the arguments against the theory of the continuity are 
destructive, not one of them a constructive explanation of the phenomena. 
Yet at the same time Della Valle has done a good Service in calling 
attention to a number of striking cases that still need explanation. One of 
these is the chromatin diminution of Ascaris; in each of five successive 
mitoses the number 4 of the chromosomes changes suddenly to about 60 
or more in the soniatic cells. Another is the numerical Variation of the 
chromosomes in the amniotic cells discribed by v. Wixiwarter; and 
another is the chromosomal Variation in the different nuclei of the endo- 
sperm sac of plants. Della Valles own observations on Salamandra 
deal with ratlier late tissue cells, not with germ cells, and he has noted that 
the chromosomal Variation of number appears to be more ample in body 
cells than in germ cells. These cases deal all with somatic cells, they do 
not in any way prove that the chromosomes of the germinal cycle are not 
persisting individualities. But they might indicate that during the body 
differentiation the chromosomes may become instable complexes and per- 
haps even cease to be continuous entities. This need not seem so surpri- 
sing, for the body cells differ from the germ cells in gradually losing the 
power of division which might be due to sonie change in the chromosomes. 
There are certainly a few positive cases where the number of chromo- 
somes of the body cells undergoes a marked change, generaUy an increase. 
Thus Della Valle may be right in part, a lability of the chromosomes 
may be a regulär phenomenon in, tissue cells. Relatively little attention 
has been devoted to the chromosomes of body cells, no general conclusion 
can yet be made about them, but there is some evidence that they may 
