Although, therefore, there is a contradiction between the unwarrantable and ill-begotten formula, “_omne vivum ex vivo_,” and the doctrines of what has been called “Spontaneous Generation”; there is no contradiction whatever between such doctrines and the only generalization which we are really warranted in arriving at, to the effect that _some representatives of every kind of organism are capable of reproducing similar organisms_. _Bacteria_, _Torulæ_, or other living things which may have been evolved _de novo_, when so evolved, multiply and reproduce just as freely as organisms that have been derived from parents. The views as to the origin of _Bacteria_ and _Torulæ_ which are most worthy of attention, may be thus enumerated:-- _a._ That they are independent organisms derived by fission or gemmation from pre-existing _Bacteria_ and _Torulæ_. _b._ That they represent subordinate stages in the life-history of other organisms (fungi), from some portion of which they have derived their origin, and into which they again tend to develop. _c._ That they may have a heterogeneous mode of origin, owing to the more complete individualization of minute particles of living matter entering into the composition of higher organisms, both animal and vegetal. _d._ That they may arise _de novo_ in certain fluids containing organic matter, independently of pre-existing living things (_Archebiosis_). I shall make some remarks concerning each of these views, though the evidence I have to adduce mainly concerns the possibility of the origin of _Bacteria_ and _Torulæ_ in the way last alluded to, viz., by _Archebiosis_. The third mode of origin is what is called _Heterogenesis_; whilst the first and second modes are the representatives of more familiar processes, included under the head of _Homogenesis_. Thus, in accordance with the first view, _Bacteria_ may be regarded as low organisms having a distinct individuality of their own and multiplying by a process of fission--thus affording instances of what I propose to term _direct Homogenesis_. Whilst, in accordance with the second view, _Bacteria_ are supposed to represent merely one stage in the life-history of higher organisms, which are therefore reproduced by an _indirect_ or cyclical process of _Homogenesis_. The possible modes of origin of _Bacteria_ and _Torulæ_ may, therefore, be tabulated as follows:-- Modes of origin { 1. Homogenesis. { _a._ Direct. of _Bacteria_ { _b._ Indirect. and { 2. Heterogenesis. _Torulæ_. { 3. Archebiosis. I. HOMOGENETIC MODE OF ORIGIN OF BACTERIA AND TORULÆ.