190 DISTRIBUTION OF THE CHROMOSOMES 
factors, since every spermatozoon receives, with the 
above exceptions, all the chromosomes (paternal and 
maternal) that the hybrid contains. On crossing the 
hybrid to either parent, it is found that the offspring 
actually are very much alike, 7.e., have all received 
practically the same factors—a striking contrast 
to the result usually obtained in ‘‘backcrosses.” 
In respect to just one character (a larval marking), 
however, the above relation does not hold, but ordi- 
nary Mendelian results are obtained, and this in turn 
corresponds with the fact that a few chromosomes 
do undergo segregation. In regard to the other char- 
acters, not only are the offspring like each other, but 
they resemble the hybrid more than either of the pure 
species, corresponding with the fact that they contain 
complete sets of chromosomes from both types. But 
they do not look just like the F, hybrid, and cor- 
respondingly one set of chromosomes is in the diploid, 
the other in the haploidnumber. This isbecause they 
receive a set of one species from both parents, but a 
set of the other species only from the hybrid parent. 
Federley also shows that when maturation takes place 
in this triploid individual one set of chromosomes 
does not undergo mating, but the others—presumably 
those in the two identical sets—do pair with each 
other, so that the total number is reduced to one bi- 
valent set, and one single set. If the paired chromo- 
somes separate and the unpaired ones divide, as oc- 
curs in the F,; hybrid, the double number of chromo- 
somes, a set of each species, will again be found in the 
sperm, as was the case in the first hybrid. In other 
