Katharine Foot and E. C. Strobell 309 
of transformation as eleven bivalents, each approximately equal in size 
to a pair of spermatogonial chromosomes. The duplicate chromosomes 
of the odgonial and spermatogonial cells may offer a demonstration of 
the unquestioned fact that the chromatin is contributed equally by both 
parents, but it seems to us this by no means involves a demonstration of 
the theory that the bivalents of the first spermatocyte are formed by a 
conjugation of these original odgonial or spermatogonial pairs. Again, 
although the univalent halves of the bivalents of the first spermatocyte 
certainly forecast a later equal division of the chromatin of each bivalent, 
we do not believe that this necessarily includes a further demonstration 
that each bivalent is in fact the two spermatogonial chromosomes with 
which it may approximately agree in size,—that these chromosomes have 
remained intact during the period in which the chromatin of all the 
chromosomes is apparently commingled. Have we a right to affirm that 
there is no readjustment of the chromatin during this period ? 
The unusual form of the two microchromosomes of Photo. 3, Plate II, 
has a very significant bearing on the question of how much meaning 
we may attach to the duplicate halves of each bivalent. It is evident 
that these two microchromosomes not only differ in form from those 
demonstrated in any of the other preparations of the same stage, but they 
are fully twice as large. As mentioned above, we might expect this 
increase in size if all the other chromosomes were proportionately larger, 
but they are in fact rather smaller than those of other preparations of 
this stage. Further, the unusual size and form of the microchromosomes 
of Photo. 3, Plate II, cannot be adequately explained on the ground of 
faulty technique for that would involve distortion and increase in size 
for all the other chromosomes of the same group and there is no evidence 
of such disturbance. 
If we must interpret these two unusual microchromosomes in accord- 
ance with the theory of the conjugation of paternal and maternal chromo- 
somes, we are forced to the conclusion that not only two individuals— 
male and female—can show exactly the same marked variation in the 
same chromosome, but that two such rare cases should unite. We avoid 
these difficulties, however, if we assume that the apparent disintegration 
of the spermatogonial chromosomes during the rest stage is a reality and 
that the chromatin emerges from the rest stage with each bivalent only 
approximately the same size as a pair of spermatogonial chromosomes. 
A comparison of our photographs—all taken at the same magnification 
—will show some ground for this assumption, that individual bivalents 
resemble only approximately a pair of spermatogonial chromosomes. 
