The _Infusoria_ reproduce their species in several ways: by a kind of budding, like plants, by sexual reproduction, and by fission—_i.e._, the spontaneous division of the animal into two parts. “By this mode of propagation,” says Dujardin, “an Infusorian is the half of the one which preceded it, the fourth of the parent of that, the eighth of its grandparent, and so on.” The process is represented in the accompanying figures, A and B being the adult, C the same in course of separation, and D after completion. “This mode of generation, however,” says Figuier, “enables us to comprehend the almost miraculous multiplication of these beings. The amount defies calculation, if we wished to be at all precise. We may, however, arrive at a proximate estimate of the number which may be derived from a single individual by this process of fission. It has been found that at the end of a month two _Stylonichiæ_ would have a progeny of more than 1,048,000 individuals, and that in a lapse of forty‐two days a single _Paramecium_ could produce much more than 1,364,000 forms like itself.” In a year it would have the proud satisfaction of being the father of an Infusorian nation! [Illustration: PROPAGATION OF AN INFUSORIAN BY SPONTANEOUS DIVISION.] Many of the _Infusoria_ are subject to metamorphoses, while others can remain long periods, and in a dried and torpid state, and then awake to action. One of the largest of these curious organisms, which sometimes actually attains to the size of the twelfth of an inch, is the _Kondylostoma patens_, remarkable for its voracity. It lives upon sea‐ weed, and is common to every shore, from the Mediterranean to the Baltic. [Illustration: KONDYLOSTOMA PATENS (MAGNIFIED 300 TIMES).] The inhabitants of the sea are, there can be no doubt, much more numerous than those of the earth. Charles Darwin has remarked that our terrestrial forests do not maintain nearly so many living beings as do marine forests in the very bosom of the ocean. Its surface and its depths, its plains and its mountains, its valleys and precipices, teem with organisms, the like of which have no counterpart on the land, and which are only partly understood to‐day, although the invention and adoption of the aquarium have greatly facilitated the study of them.