of the occurrence of spontaneous generation to
seek evidence for their hypothesis only among the parasites and the
lowest and minutest organisms. It is just fifty years since Schwann
and others proved that, even with respect to them, the supposed
evidence of abiogenesis was untrustworthy.

During the present epoch, the question, whether living matter can be
produced in any other way than by the physiological activity of other
living matter, has been discussed afresh with great vigor; and the
problem has been investigated by experimental methods of a precision
and refinement unknown to previous investigators. The result is that
the evidence in favor of abiogenesis has utterly broken down, in every
case which has been properly tested. So far as the lowest and minutest
organisms are concerned, it has been proved that they never make their
appearance, if those precautions by which their germs are certainly
excluded are taken. And, in regard to parasites, every case which
seemed to make for their generation from the substance of the animal,
or plant, which they infest has been proved to have a totally
different significance. Whether not-living matter may pass, or ever
has, under any conditions, passed into living matter, without the
agency of pre-existing living matter, necessarily remains an open
question; all that can be said is that it does not undergo this
metamorphosis under any known conditions. Those who take a monistic
view of the physical world may fairly hold abiogenesis as a pious
opinion, supported by analogy and defended by our ignorance. But, as
matters stand, it is equally justifiable to regard the physical world
as a sort of dual monarchy. The kingdoms of living matter and of
not-living matter are under one system of laws, and there is a perfect
freedom of exchange and transit from one to the other. But no claim to
biological nationality is valid except birth.

[Sidenote: Morphology.]

In the department of anatomy and development, a host of accurate and
patient inquirers, aided by novel methods of preparation, which
enable the anatomist to exhaust the details of visible structure and
to reproduce them with geometrical precision, have investigated every
important group of living animals and plants, no less than the fossil
relics of former faunae and florae. An enormous addition has thus been
made to our knowledge, especially of the lower forms of life, and it
may be said that morphology, however inexhausti