more than six or seven minutes. At this rate, a
single _Heteromita_ would give rise to a thousand like itself in the
course of an hour, to about a million in two hours, and to a number
greater than the generally assumed number of human beings now living in
the world in three hours; or, if we give each _Heteromita_ an hour's
enjoyment of individual existence, the same result will be obtained in
about a day. The apparent suddenness of the appearance of multitudes of
such organisms as these in any nutritive fluid to which one obtains
access is thus easily explained.

During these processes of multiplication by fission, the _Heteromita_
remains active; but sometimes another mode of fission occurs. The body
becomes rounded and quiescent, or nearly so; and, while in this resting
state, divides into two portions, each of which is rapidly converted into
an active _Heteromita_.

A still more remarkable phenomenon is that kind of multiplication which
is preceded by the union of two monads, by a process which is termed
_conjugation_. Two active _Heteromitoe_ become applied to one another,
and then slowly and gradually coalesce into one body. The two nuclei run
into one; and the mass resulting from the conjugation of the two
_Heteromitoe_, thus fused together, has a triangular form. The two pairs
of cilia are to be seen, for some time, at two of the angles, which
answer to the small ends of the conjoined monads; but they ultimately
vanish, and the twin organism, in which all visible traces of
organisation have disappeared, falls into a state of rest. Sudden wave-
like movements of its substance next occur; and, in a short time, the
apices of the triangular mass burst, and give exit to a dense yellowish,
glairy fluid, filled with minute granules. This process, which, it will
be observed, involves the actual confluence and mixture of the substance
of two distinct organisms, is effected in the space of about two hours.

The authors whom I quote say that they "cannot express" the excessive
minuteness of the granules in question, and they estimate their diameter
at less than 1/200000 of an inch. Under the highest powers of the
microscope, at present applicable, such specks are hardly discernible.
Nevertheless, particles of this size are massive when compared to
physical molecules; whence there is no reason to doubt that each, small
as it is, may have a molecular structure sufficiently complex to give
rise to the phenomena of life. And