576 THE AMERICAN NATURALIST. (VoL. XXXIX. 
cussion of “ Reduction of Chromosomes ”). The’ important 
point for us is the belief that the appearance of the bivalent 
chromosomes during reduction is due to the temporary union of 
somatic or sporophytic chromosomes in pairs and further that 
the reduciag divisions distribute the members of the pair, which 
are believed to be descendants of the maternal and paternal 
chromosomes of the previous generation, as organic entities to 
the generation which is to follow. 
It is difficult to overestimate the importance of this general- 
ization. If the program prove to be correct as stated above and 
if the chromosome is established beyond doubt as a self-perpet- 
uating organ of the cell and a bearer of hereditary characters 
we have then the possibility of studying the actual manner in 
which these structures are passed on from one generation to the 
next and perhaps determine the ratios or combinations through 
which the distribution is effected. The difficulty of making an 
exact determination of ratios in any form so far studied lies in 
our inability to distinguish the chromosomes of maternal and 
paternal origin. There is much evidence that the pairs of 
somatic and sporophytic elements, which form the bivalent 
chromosomes of the reduction mitoses of animals and plants 
respectively, are of different parentage but we do not know 
whether or not there is any rule in the arrangement of the pairs 
on the spindles of these mitoses although this is hardly to be 
expected. Cannon (:02, :03a) and others have held that the 
mitoses of reduction brought about the complete separation of 
the maternal and paternal chromosomes so that two of the 
resultant four nuclei contain chromosomes from one parent and 
two from the other, and the germ cells are in consequence abso- 
/utely pure in character. But this view was soon shown by Sut- 
ton (:03, p. 233; accepted by Cannon, :03b) to be at variance 
with the facts of breeding for if germ cells of hybrids are a£so- 
/utely pure there could be no further change by cross-breeding 
and the first cross would be repeated over and over again with- 
out any divergence from the type, which is contrary to experi- 
ence and fact. The pairs of chromosomes are probably arranged 
in every possible order and the maternal and paternal elements 
are distributed in every possible combination by the reducing 
