Saltatory Evolution 23 
medusoid from a free-swimming animal to a mere brood-sac (gono- 
phore) is not sudden and saltatory, but occurs by imperceptible 
modifications throughout hundreds of years, as we can learn from 
the numerous stages of the process of degeneration persisting at the 
same time in different species. 
If, then, the degeneration to a simple brood-sac takes place only 
by very slow transitions, each stage of which may last for centuries, 
how could the much more complex ascending 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 repre- 
sent 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 
