ON THE TENDENCY OF VARIETIES, ETO, 27 
prejudiced belief in the stability of species. Equally 
general, however, is the belief in what are called 
“permanent or true varieties,”—races of animals 
which continually propagate their like, but which 
differ so slightly (although constantly) from some 
other race, that the one is considered to be a variety 
of the other. Which is the variety and which the 
original species, there is generally no means of de- 
termining, except in those rare cases in which the 
one race has been known to produce an offspring 
unlike itself and resembling the other. This, how- 
ever, would seem quite incompatible with the “ per- 
manent invariability of species,” but the difficulty is 
overcome by assuming that such varieties have strict 
limits, and can never again vary further from the 
original type, although they may return to it, which, 
from the analogy of the domesticated animals, is 
considered to be highly probable, if not certainly 
proved. 
It will be observed that this argument rests en- 
tirely on the assumption, that varieties occurring in 
a state of nature are in all respects analogous to or 
even identical with those of domestic animals, and 
are governed by the same laws as regards their per- 
manence or further variation. But it is the object 
of the present paper to show that this assumption is 
altogether false, that there is a general principle in 
nature which will cause many varieties to survive 
the parent species, and to give rise to successive 
variations departing further and further from the 
