nd bud
generation, though often counteracted by various known and unknown causes.
Secondly, reversion or atavism, which depends on transmission and
development being distinct powers: it acts in various degrees and manners
through both seminal and bud generation. Thirdly, prepotency of
transmission, which may be confined to one sex, or be common to both sexes
of the prepotent form. Fourthly, transmission, limited by sex, generally to
the same sex in which the inherited character first appeared. Fifthly,
inheritance at corresponding periods of life, with some tendency to the
earlier development of the inherited character. In these laws of
Inheritance, as displayed under domestication, we see an ample provision
for the production, through variability and natural selection, of new
specific forms.

* * * * *

{85}

CHAPTER XV.

ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED
BREEDS--WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE
ABSORBS THE OTHER--THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY OF
TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION--ALL
ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS--ON CERTAIN
CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE
SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE MODIFICATION OF OLD RACES,
AND THE FORMATION OF NEW RACES, BY CROSSING--SOME CROSSED RACES HAVE
BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF DISTINCT
SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.

In the two previous chapters, when discussing reversion and prepotency, I
was necessarily led to give many facts on crossing. In the present chapter
I shall consider the part which crossing plays in two opposed
directions,--firstly, in obliterating characters, and consequently in
preventing the formation of new races; and secondly, in the modification of
old races, or in the formation of new and intermediate races, by a
combination of characters. I shall also show that certain characters are
incapable of fusion.

The effects of free or uncontrolled breeding between the members of the
same variety or of closely allied varieties are important; but are so
obvious that they need not be discussed at much length. It is free
intercrossing which chiefly gives uniformity, both under nature and under
domestication, to the individuals of the same speci