Aquatic Lite 37 
Comments 
Inasmuch as the mule, our most fa- 
miliar hybrid, is sterile, the opinion seems 
to prevail among the uninformed that all 
crosses are sterile. No law has yet been 
formulated to cover the question of fer- 
tility. While fertile hybrids are not com- 
mon, the capacity for hybridization in the 
first generation is widespread. Fertile 
hybrids have been secured by crossing 
the Virginia deer and the Ceylon deer, 
the American bison and domestic cattle, 
the brook trout and the Charr, the com- 
mon goldfish and the carp. The Shu- 
bunkin is a hybrid of the Chinese Calico 
Telescope Goldfish and the Wakin, the 
Japanese form of the common goldfish. 
And now we have the poecilid hybrid. 
Had the peas used by Mendel produced 
sterile hybrids, his work, at least with the 
particular species, would have ended. In- 
deed, it is in the behavior of the off- 
spring of the first hybrid generation that 
Mendel’s law becomes apparent. His re- 
sults have been confirmed and extended 
by workers, both for plants and animals, 
but much is still uncertain concerning 
both the extent to which the principles 
may be found to occur and also the fun- 
damental physical basis on which they 
depend. 
The interesting feature of Mr. Web- 
ber’s article has to do with the emphasis 
he places on the absence of a reversional 
tendency. It is not clear whether he 
implies that the hybrids were all of a type 
which resembled neither parent, or 
whether there was a reversional tendency, 
but not to such a degree that any of the 
offspring were counterparts of the par- 
ents of the first hybrid generation. An 
absolute reversion in such a cross would 
be astounding. The parent species dif- 
fer in colors and form and in all other 
characters save those which place them 
in related genera in the family PorciLt- 
IDAK. ‘Too many factors are involved in 
such a cross to permit an absolute rever- 
sion. Mendel, in his most easily ex- 
plained experiments, selected species that 
differed essentially in but one character ; 
size, for example. One parent was tall, 
the other a dwarf. Otherwise they were 
much alike, so but one character, size, 
was to be studied in the first and suc- 
ceeding generations, and this without the 
confusion that would result were other 
factors also opposed. The same applies 
to an animal cross between a black and a 
white, the colors being the opposing char- 
acters. When animals of sundry diverg- 
ent characters are crossed, many factors 
are involved, not only of the immediate 
subjects, but of their ancestors. ‘Thus 
some hybrids exhibit characters that are 
obviously those of ancestors, which, per- 
haps, may be non-existent today, as in the 
case of Ewart’s experiments with the 
zebras. In certain cases it may happen 
that when a black mouse is bred to an 
albino, each from a strain breeding true 
to its color, the result will be a reversion 
to the wild gray color. This is due to 
the bringing together of complimentary 
factors that, in the course of evolution, 
had become separated. 
The writer has examined numerous 
specimens of the hybrid, Xiphophorus 
hellert X Platypoecilus maculata rubra, 
none of which, however, were bred by 
the gentlemen named by Mr. Webber. 
The dominants were unlike either parent 
other than in shape, which was interme- 
diate, and in a tendency toward the devel- 
opment of the lower rays of the caudal 
fin into the “sword” that is characteristic 
of the male Xiphophorus. The recessive 
can be described as resembling a pale 
female Xiphophorus, which, also, in cer- 
tain cases, 1s said to develop a “‘sword- 
tail.’ The proportion of dominants and 
recessives exhibiting the ‘‘sword-tail”’ 
character does not seem to have been 
accurately recorded, so it is yet to be 
