The Presidential Address. 85
the species is protected from Nature's strife, it may persist
unaltered or with only slight modification throughout whole
geological periods, as we see in the numerous low forms of
aquatic life, and higher in the scale in such types as Lepido-
siren and Ornithorhynchus, which Darwin speaks of as "living
fossils."26 Or again, through parasitism or other causes, a
species may be driven to a mode of life in which high
organisation is not only useless, but may be actually detri-
mental to its possessor. In such cases natural selection,
having only the good of the species in view, would bring
about a more lowly-organised condition in the adult animal,
while the younger stages, by the law of homochronic heredity,
would retain the higher structure of the ancestral form.
This principle of "degeneration" is seen in such groups as
the Ascidians, the parent-stock of all the vertebrate animals;
in the barnacles, which are degenerate Crustacea; and in the
Mexican Axolotl. The development of Darwinism in this
direction will be found in works by Anton Dohrn27 and Prof.
E. Ray Lankester.28
Before concluding this necessarily imperfect sketch of
Darwin's chief work, there remain a few considerations to
which I should like to direct attention. I may remind you,
with reference to the various objections that have from time
to time been urged against the theory of selection, that there
has not been a more candid critic of this theory than Mr.
Darwin himself, and in point of fact it is not going too far to
say that hardly any difficulty of importance has been raised
which was not suggested in the 'Origin of Species.' I will,
with your permission, dwell briefly upon one or two objections
which are still occasionally to be heard.
Variability, the basic factor of species-transformation, is
26 Just as this Address was completed there appeared in 'Nature' an
interesting article by Prof. Hubrecht, in which the subject of persistent
forms of life is treated in a somewhat novel way, under the title of "The
Hypothesis of Accelerated Development by Primogeniture, and its place
in the Theory of Evolution." Vol. xxvii., pp. 279 and 301.
27 'Der Ursprung der Wirbelthiere und das Princip des Functionswech-
sels,' Leipzig, 1875.
28 'Degeneration, a Chapter in Darwinism,' Macmillan, 1880.