DISTRIBUTION OF THE CHROMOSOMES 189 
foreign cytoplasm. In the maturation a few of the 
chromosomes seem at times to unite in pairs, but 
most of them fail to do so, so that while the number 
of the chromosomes at the first maturation division 
is slightly less than the full number it is much more 
than half of that number. Different types of 
hybrids behave slightly differently in respect to the 
extent to which union in pairs takes place. The 
failure to unite indicates that in normal maturation 
homologous chromosomes mate with each other, 
for here there are few or no chromosomes that are 
strictly homologous and yet there is just as much 
opportunity as in normal maturation for non- 
homologous chromosomes from the same parent to 
unite. | 
When the first spermatocyte division takes place 
in the hybrid, all the unmated chromosomes divide, 
but the few chromosomes that are mated pre- 
sumably separate. Consequently each of the daugh- 
ter cells has the double number of chromosomes 
(a set from each parent species), except for the few 
chromosomes that had been united in pairs. At 
the second maturation division the chromosomes 
again divide, so that the spermatozoa too should 
receive nearly the double number of chromosomes, 
one set from one species, the other set from the other 
species. 
If, then, the factors are contained in the chromo- 
somes, we should expect that, except for any factors 
in the few chromosomes that mate and separate, the 
hybrid would transmit, to all its offspring the same 
