evolution possibly have taken
place by sudden leaps? I regard this argument as capable of further
extension, for wherever in nature we come upon degeneration, it is
taking place by minute steps and with a slowness that makes it not
directly perceptible, and I believe that this in itself justifies us in
concluding that THE SAME MUST BE TRUE OF ASCENDING evolution. But in the
latter case the goal can seldom be distinctly recognised while in cases
of degeneration the starting-point of the process can often be inferred,
because several nearly related species may represent different stages.

In recent years Bateson in particular has championed the idea of
saltatory, or so-called discontinuous evolution, and has collected a
number of cases in which more or less marked variations have suddenly
appeared. These are taken for the most part from among domesticated
animals which have been bred and crossed for a long time, and it is
hardly to be wondered at that their much mixed and much influenced
germ-plasm should, under certain conditions, give rise to remarkable
phenomena, often indeed producing forms which are strongly suggestive of
monstrosities, and which would undoubtedly not survive in free nature,
unprotected by man. I should regard such cases as due to an intensified
germinal selection--though this is to anticipate a little--and from this
point of view it cannot be denied that they have a special interest. But
they seem to me to have no significance as far as the transformation
of species is concerned, if only because of the extreme rarity of their
occurrence.

There are, however, many variations which have appeared in a sudden and
saltatory manner, and some of these Darwin pointed out and discussed
in detail: the copper beech, the weeping trees, the oak with "fern-like
leaves," certain garden-flowers, etc. But none of them have persisted in
free nature, or evolved into permanent types.

On the other hand, wherever enduring types have arisen, we find traces
of a gradual origin by successive stages, even if, at first sight, their
origin may appear to have been sudden. This is the case with SEASONAL
DIMORPHISM, the first known cases of which exhibited marked differences
between the two generations, the winter and the summer brood. Take
for instance the much discussed and studied form Vanessa (Araschnia)
levana-prorsa. Here the differences between the two forms are so great
and so apparently disconnected, that one might al