AND OF HYBRID PIGEONS. 
35 
spermatogenesis from the first part of this paper. Only the 
modifications and irregularities which mark the hybrid will be 
considered herd. 
The term hybrid is used in conformity with the definition 
given in the Century Dictionary which pronounces as hybrids 
such animals or plants as result from a cross of two forms 
noticeably different. Unsatisfactory as the definition is, it 
seems to be as accurate as it can be made. The objection, of 
course, is that it is uncertain how noticeably different two forms 
must be to be regarded as having individualities distinct enough 
to produce hybrid offspring when crossed. 
In the pigeon, some crosses are fertile, others are not. The 
sterile birds show a greater or less degeneration of the germinal 
cells. In the hybrid forms studied, the general rule seemed to 
be that the more divergent the parent forms, the more marked 
was the degeneration of the germinal cells. 
From parents which differ very widely in structure or habits, 
there is greater difficulty in securing female hybrids than male. 
The meaning of this is as yet a mystery. So far, I have been 
able to get but one female for microscopical examination. On 
the other ‘hand, I have had six males, the offspring of very dis¬ 
tinct species. These were all sterile forms. 
From the hybrid offspring of the common ring dove (Turtur 
risorius) and the white ring dove (Columba alba), a large number 
of sections were made for microscopical study. These two 
forms are perfectly fertile when crossed and the fertility of their 
offspring seems in no wise diminished. The latter are both 
fertile one with another, and with the parent species. The 
germ cells show some of the same phenomena as those of the 
sterile birds, only in a much less marked degree. 
Offspring of the common ring dove when crossed with the 
white ring dove are brown in color. One member of the result¬ 
ing pair is frequently a few shades lighter in color than the 
other. In the next or third generation there is generally a 
return to the original colors of the grandparents; one of the 
young is white, the other brown. Occasionally both of the 
young are brown or, less frequently, both white. There is a 
marked tendency for the white ones to be female and the brown 
ones male. 
