ASPECTS OF BIOLOGY AND METHOD OF BIOLOGICAL STUDY. 41 
to all intents and purposes infinite. It is true that in a few cases 
a continuous series of forms regularly passing from lower to higher 
degrees of specialization, and very probably connected to another 
by direct descent, may be followed through long geological peri- 
- ods, as, for example, the graduated series already alluded to, which 
may be traced between certain mammals of the Eocene and others 
living in our own time, as well as the very low forms which have 
come down to us apparently unmodified from the epoch of the 
Chalk. But incalculably great as are these periods, they are but 
as the swing of the pendulum in the millennium, when compared 
to the time which has elapsed since the first animalization of our 
globe. 
Is the faculty of reproduction so wonderfully tenacious as all 
this, that through periods of inconceivable duration, and exposed 
to influences the most intense and the most varied, it has still 
come down to us in an unbroken stream? Have the strongest 
which had survived in the struggle for existence necessarily 
handed down to the strongest which should follow them the power 
of continuing as a perpetual heirloom the life which they had 
themselves inherited? Or have there been many total extinctions 
and many renewals of life—a succession of genealogical trees, the 
earlier ones becoming old and decayed, and dying out, and their 
place taken by new ones which have no kinship with the others? 
Or, finally, is the doctrine of evolution only a working hypothesis 
which, like an algebraic fiction, may yet be of inestimable value as 
an instrument of research? For as the higher calculus becomes 
to the physical inquirer a power by which he unfolds the laws of 
the inorganic world, so may the hypothesis of evolution, though 
only a hypothesis, furnish the biologist with a key to the order and 
hidden forces of the world of life. And what Leibnitz and New- 
ton and Hamilton have been to the physicist, is it not that which 
Darwin has been to the biologist? 
But even accepting as a great truth the doctrine of evolution, 
let us not attribute to it more than it can justly claim. No vali 
evidence has yet been adduced to lead us to believe that inorganic 
matter has become transformed into living, otherwise than through 
the agency of a preéxisting organism, and there remains a resid- 
ual phenomenon still entirely unaccounted for. No physical hy- 
pothesis founded on any indisputable fact has yet explained the 
origin of the primordial protoplasm, and, above all, of its marvel- 
lous properties which render evolution possible. ; 
