36 
SPERMATOGENESIS OF NORMAL 
Inasmuch as doves produce but two young at a brood, it 
would require a long period of time to secure numbers sufficient 
to arrive at satisfactory conclusions regarding the percentage 
of actual reversion to the original species. From the one char¬ 
acter of color one might be led to infer that in the third gener¬ 
ation there is in the majority of cases a reversion to the grand¬ 
parent types, since the offspring are ususally one white and one 
brown. This conclusion does not necessarily follow, however, 
for we have no means of knowing whether the brown one gets 
its color from a return to the brown grandparent or directly 
from the parents of the second generation, both of which are 
brown. So far as the writer has carried his experiments, the 
indications are that on the whole there are more brown than 
white birds in the third generation, and this points to the con¬ 
clusion that in the brown birds we may have both intermediate 
forms like the hybrids of the second generation and forms 
which have reverted to the brown grandparent, as the white 
doves have seemingly returned to the white grandparent. On 
the other hand, it does not necessarily follow that all white 
birds seen in the third generation have, reverted entirely to the 
white ancestor. As has been mentioned, one of the doves of 
the original hybrid pair is often a lighter shade of brown than 
the other, hence the birds do not show the same degree of inter¬ 
mediacy. The birds of this generation, then, might mate in 
such a way that the offspring could exhibit the ancestral white 
while yet remaining intermediate in other characters. As we 
shall see in the conclusions from the study of the germ cells of 
hybrids, there are certain phenomena in the germ cells which 
apparently afford us a definite physical basis for the produc¬ 
tion of intermediate forms and for returns to pure ancestral 
species. From this basis there must necessarily be a greater 
number of intermediate forms in the offspring of hybrids than 
there are reversions to the respective ancestral species. 
Of the sterile hybrids, whether male or female, the sexual 
products were abnormal. As already stated, only one such 
female was examined. The facts observed concerning her will 
be briefly related later when the individual record of each form 
examined is given. Certain abnormalities exist in some phases 
of the fertile hybrid spermatogenesis as well as in the sterile 
