548
One of the most interesting facts which lend support to
this view of the backward development of the axolotl is
the discovery that the axolotl has a rudimentary inter
maxillary gland furnishing a glutinous secretion, and
which serves to aid the capture of insect-prey. Now, as
this gland exists in a perfect shape in all land amphibians,
but is absent in gill-possessing forms, its presence in the
gilled axolotls would seem to indicate that these animals
retain the gland as a legacy from the higher or ambly-
stoma stage, from which they are believed by Dr. Weismann
to be descended and retrograded.*
So far as my present argument is concerned, it is un
necessary that we should determine which is the correct
view with respect to the actual and existing axolotl. If it
be a progressive stage, it represents a stage in the evolu
tion of the race awaiting further development. If it be a
retrogressive form, we are either deprived of any evidence
whatever of the progressive evolution of the race, or we
must accept the axolotl conditions as more or less repre
senting a half-way house past which the amblystoma race
must have travelled—back to which the amblystoma has
reverted, with some characteristics inherited from its
amblystoma parents. For the purposes of the present
argument, either of the above suppositions may be enter
tained. What we are specially concerned to know is
whether we can find any trace whatever of the action of
Natural Selection in this connection.
Dr. Wilson, who believes that the axolotl is a larval
form, refers the change to transforming influence. The
case of the axolotl, he says, illustrates powerfully the
effects of a change of surroundings in metamorphosing a
species. A succession of dry seasons, operating in the
Wilson, p. 248.