58 
Katharine Foot and E. C. Strobell 
spermatocyte representing 2 instcad of a single cliromosonie. E\ädence 
can be claimed for this in the second spermatocyte in photo 32, in whicli 
each half of this large chroniosonie is coinposed of two distinct bodies. 
But if such evidence is valid, then it might be claimed that in photo 30 
each half of this chromosome is composed of 3 chromosomes, for three 
bodies are as distinctly shown in this photograph as are the two in the 
same chromosome of photo 32. 
One frequently finds evidence that the chromosome itself is a Segre- 
gation of smaller imits and in some cases the subdivisions show a rather 
striking regularity in size. We fonnd this to be frequently the case in 
Euschistus variolarius. In studying the photographs of a large number 
of chromosome groups from the same embryo — in one case more than 
one hundred and fifty from the same embryo — we were impressed by 
the frequent recurrence of a constriction at a quite definite point in 
either one or both chromosomes of a pair, and frequently 3 or 4 chromo- 
somes showed a like constriction. In many cases the constricted part 
becomes entirely separated from the mother chromosome, and as these 
are clearly detached parts of whole chromosomes, they may be caUed 
chromosome fragments or chromomeres. 
In the cases in which they have become independent of the mother 
chromosome they may behave as independent chromosomes even divid- 
ing independently in mitosis. "When they have separated from the mother 
chromosome and are independent, they are then astonishingly like the 
supernumerary chromosomes described and figured by Wilson and 
Stevens, but they cannot be interpreted as the same structure for both 
these authors find the number constant in the same indi\'idual. 
In describing the supernumerary chromosomes of Metapodius 
AVilson '09 says, “The chromosomes in question are the ones which 
I have called the ‘supernumeraries’. In behavior they show an 
unmistakable similarity to the idiochromosomes; and for reasons 
given beyond I believe them to be nothing other than additional 
small idiochromosomes, the presence of which has resulted from irre- 
gularities of distribution of the idiochromosomes in preceding genera- 
tions.” Pg. 150. 
After stating that the number of supernumerary chromosomes is 
“a characteristic feature of the individual in which it occurs”, he adds, 
“I do not mean to assert that there is absolutely no fluctuation in the 
individual . . . but the latter are so rare that they may practically be 
disregarded”. This conclusion as to the constancy in the number of 
supernumerary chromosomes for each individual is supported by Ste- 
