AND OF HYBRID PIGEONS. 
27 
varied distribution of the univalent components than the sever¬ 
ing of an ordinary bivalent chromosome. The result would be 
greater diversity among the ultimate germ cells than would 
otherwise occur, and this would appear later in the form of 
greater variation among the offspring. The quadrivalent 
chromosomes could divide transversely in such a direction as 
to separate maternal and paternal chromosomes. This would 
seem to be the prevalent mode of division in hybrids, provided 
their respective parental qualities have not already been set 
apart in the primary spermatocytes. If the division of the 
quadrivalent chromosome, be a transverse division at right 
angles to the direction just indicated, each ultimate germ cell 
would include both maternal and paternal chromatin. Both 
kinds of division occur, perhaps, in normal forms—possibly 
both kinds in the same cell. It can be seen at a glance that the 
number of possible combinations of qualities from egg cell and 
sperm cell at the time of fertilization would be considerably in¬ 
creased if both kinds of division take place. Offspring could 
possess the qualities of one grandparent on the paternal side to 
the exclusion of the other or exhibit the characters of each in 
equal proportion or in varying proportions. The same would 
be true, of course, with respect to the grandparents on the 
maternal side, provided the maturation of the egg has brought 
about a distribution of chromosomes similar to that seen in the 
spermatozoon. The fact that two lines of ancestry are merged 
in ordinary breeding complicates the matter, but it can readily 
be seen that such an arrangement of the chromosomes for the 
last division as is here indicated would add to the chances for 
variation in the offspring. The possibility presents itself then, 
that the second fusion of chromosomes as seen in the secondary 
spermatocytes is for the purpose of producing greater varia¬ 
tion. This interpretation is, of course, as yet little more than a 
suggestion, and it is offered merely as an interesting possibility 
and as the only explanation the writer has been able to conceive 
of concerning the remarkable diminution in the number of the 
chromosomes from sixteen to four. 
