struggle between the parent species and more or less
nascent varieties.
When a whole species undergoes considerable variation,
it becomes a new species. This seems to be assumed by-
Mr. Wallace. He describes the process by which he
conceives that the adaptation of a species to new con
ditions may have been brought about. “ But,” he adds,
“ it will now be a different creature.”* And it would
seem to follow from this, that the ancestral form has
become an extinct species ; so that, in this case, the
extinction of species is the necessary prelude of the trans
formation of species. A different creature would naturally
be classified in a different species to that from which it
had arisen, if we knew nothing of its origin. But will
this knowledge make any difference ? It certainly does
with some persons, who have provided us with very differ
ent definitions of the word species. The old fashioned
idea of species is that God made so many different kinds
of animals to be fruitful inter se, to multiply and to repro
duce offspring after their own typical likeness. The test
of likeness is not, however, held very rigidly. It is
assumed that a species may be variable but yet immut
able, as indeed is the fact in some cases. But when, in
spite of this latitude of interpretation, it is found that
considerable changes take place in a given race, quite
sufficient to constitute the offspring a new species—if we
judge only by the comparative likeness or unlikeness—then
the definition is modified altogether; the test of a true
species is not to be found, we are told, in similarity or dis
similarity, but in the continuous fertility of the offspring.
Now, it is quite clear that these definitions exclude one
another ; they are not capable of being harmonised. Exact
U
* Contributions, p. j/o.