34 THE ORIGIN OF SPECIES Ir 
either in form or in structure. There is always a 
certain amount of deviation, not only from the 
precise characters of a single parent, but when, as _ 
in most animals and many plants, the sexes are 
lodged in distinct individuals, from an exact mean 
between the two parents. And indeed, on 
general principles, this slight deviation seems as — 
intelligible as the general similarity, if we reflect 
how complex the co-operating “ bundles of forces ” 
are, and how improbable it is that, in any case, 
their true resultant shall coincide with any mean 
between the more obvious characters of the two 
parents. Whatever be its cause, however, the 
co-existence of this tendency to minor variation 
with the ne tendency to general similarity, is of vast 
importance in its bearing on the > question of th of the 
origin of species. : 
As a general rule, the extent to which an 
offspring differs from its parent is slight enough; 
but, occasionally, the amount of difference is much 
more strongly marked, and then the divergent 
offspring receives the name of a Variety. Multi- 
tudes, of what there is every reason to believe are — 
such varieties, are known, but the origin of very 
few has been accurately recorded, and of these we 
will select two as more especially illustrative of 
the main features of variation. The first of them — 
is that of the “Ancon” or “Otter” sheep, of 
which a careful account is given by Colonel 
David Humphreys, F.R.S. in a letter to Sir 
ie nat a 
SN 6 asi 9 Saat Fa 
