That the _Bacteria_ which reproduce should be in a comparatively quiescent condition, seems not difficult to understand. Such rudimentary organisms do not appear to possess cilia or other locomotory appendages: their movements are, therefore, in all probability dependent upon the mere molecular changes which are taking place within them, and upon which their life and nutrition depend. The process of fission must, however, be considered as the result of a new effort at equilibrium, which has, perhaps, been necessitated by molecular changes that have occurred during a preceding period of growth. The living matter which is no longer able to exist round a single centre, re-arranges itself around two centres,--as a result of which, fission occurs. It seems only natural, therefore, that whilst this active work of molecular re-arrangement is going on, those other molecular movements which occasion the actual locomotion of the organism from place to place, should be more or less interfered with. This is the one and only mode of multiplication of _Bacteria_ and of _Torulæ_ which is actually known to occur; and such a limitation is in accordance with the more general fact, that processes of fission or gemmation are the only means of reproduction that are known to occur in the lower kinds of organisms, belonging to the PROTISTIC kingdom. However well this process of fission may have been established, as a frequent mode of reproduction of _Bacteria_, such a fact does not lend any support to the notion that these are necessarily distinct and independent organisms. _Torulæ_ (of which beer-yeast is the most familiar example) may similarly undergo this process of mere vegetative repetition to an indefinite extent, whilst only some of the products develop into fungi. The gonidia of lichens may also reproduce indefinitely in this fashion, and only some of the products of multiplication may go on to the production of lichens similar to that from which the gonidia had been derived. It is a fact, however, admitted by many, and which any patient microscopist is capable of verifying for himself, that some _Bacteria_ do develop into _Leptothrix_ filaments, and that these are capable of passing into a dissepimented mycelial structure of larger size and undoubtedly fungus nature--from which fructification of various kinds may be produced. Some _Bacteria_ may therefore develop into some fungi, just as certainly as some _Torulæ_ may develop into other fungi, or, just as surely as some multiplying gonidia may develop into lichens.