[5] Notwithstanding what Professor Huxley has said, I believe it to be almost certain that in many cases _Bacteria_ exist in a solution in which there are neither _Torulæ_ nor developed fungi. And, on the other hand, I have seen fungi growing in a simple (boiled) solution of tartrate of ammonia, for weeks together, without the appearance of _Bacteria_ or the occurrence of any turbidity of the solution; and on two or three occasions I have seen _Torulæ_ swarming in an infusion without the presence of _Bacteria_. But, with reference to these supposed cases of budding, and also to those others in which the contents of a spore or sporangium break up into what Professor Hallier calls “micrococci” (which are generally incipient _Bacteria_), it would be difficult for us to decide whether such processes are normal or abnormal. When we have to do with such organisms, in fact, there may be the nicest transitions between what is called Homogenesis, and what, when occurring in other organisms, we term Heterogenesis. It may be that the production of such “micrococci” from the spore or sporangium of the fungus is not an invariable incident in the life-history of the species, but rather an occasional result of the influence of unusual conditions, or of failing vigour on the part of the organism. In this latter case we should have to do with a process of Heterogenesis; although, as I have just stated, in respect to such low and changeable organisms, scarcely any distinct line of demarcation can be drawn between Homogenesis and Heterogenesis. The evidence seems, therefore, against the notion that _Bacteria_ or _Torulæ_ are ordinary, independent living things, which merely reproduce their like. That some _Bacteria_ are produced from pre-existing _Bacteria_, just as some _Torulæ_ are derived from pre-existing _Torulæ_, may, it is true, be considered as settled. But, so far as we have yet considered the subject, there may be just as good evidence to show that _Bacteria_ and _Torulæ_ are capable of arising _de novo_, as there is that some of them are capable of developing into fungi. If this were the case, such types could only be regarded as the most common forms assumed by new-born specks of living matter; and, by reason of their origin--which would entail an absence of all hereditary predisposition--they might be supposed to be capable of assuming higher developmental forms. Now, as a matter of fact, worthy of arresting our attention, we do find that some _Bacteria_ are capable of growing into _Leptothrix_, whilst this is able to develop continuously into a fungus; just as we also know that some _Torulæ_ are capable of growing into other fungi. Should it be established, therefore, that _Bacteria_ and _Torulæ_ are capable of arising _de novo_, the facts concerning their mutability are harmonious enough with theoretical indications.