Katharine Foot and E. C. Strobell 307 
space between the arms could produce the forms of Photos. 19 and 20. 
A third exception to the well-defined cross form is seen in the largest 
chromosome of Photo. 7, Plate IT, but there is no evidence that this does 
not represent merely a condensation of the two halves of a cross-shaped 
chromosome. 
Quite as marked a variation in form as well as size may be demon- 
strated also for the microchromosomes. The extent of such variation 
can be appreciated by comparing the microchromosomes of the early 
prophase of Photos. 2 and 3, Plate IJ. Those of Photo. 3 besides being 
different in form appear to be fully twice as large as those of Photo. 2. 
We might expect this if all the other chromosomes were proportionately 
larger, but in fact they are, if anything, smaller than those of Photo. 2. 
Such individual and independent variation in size seems to challenge us 
to show a like variation in both the small spermatogonial chromosomes, 
or it suggests that although the chromatin may emerge from the resting 
spermatocyte showing the typical number of subdivisions, the size rela- 
tions of these chromosome units may be only approximately maintained. 
The thread-like microchromosomes of Photo. 3, Plate II, seem to offer 
an explanation of Montgomery’s observations as to the difference in size 
of these two chromosomes. <A section showing a transverse view of one 
and a longitudinal view of the other would demonstrate the two showing 
a marked inequality in size. Even a smear may show a shght inequality 
in the size of these chromosomes, but in such cases one of them is ob- 
viously more condensed than the other. This is shown in Photo. 4, Plate 
II, but a comparison of the large number of photographs in which the 
two are clearly defined proves that in our preparations the two univalent 
halves of this bivalent are equal in size. 
In considering the individuality of the chromosomes, it is an inter- 
esting fact that the one chromosome which divides longitudinally in the 
first division, divides transversely in the second, and it is a point in 
support of the theory that a longitudinal and transverse separation of 
each chromosome may have an important. significance. 
The history of the eccentric chromosome indicates that we may rely on 
the evidence of the prophase in determining the plane of the next divi- 
sion, for example, the prophases of the first spermatocyte of Photos. 21 
to 24, Plate I, clearly predict that in the first spindle the eccentric will 
divide longitudimally and the other chromosomes transversely and this 
proves to be true. The fact that this can be demonstrated gives us good 
reason to question certain apparent contradictions, e. g., the form of the 
chromosomes of. Photos. 19 to 22, Plate III, would indicate that those 
