But, as I have before indicated, although it is quite true that some _Bacteria_ develop into fungi, such forms may constitute no necessary links in the life-history of other fungi. I have suggested that in those (occasional) cases in which they do occur as links in the life-history of fungi, there is room for doubt whether these _Bacteria_ are to be considered as normal products, or as abnormal results (heterogeneous offcasts), brought about by some unusual conditions acting upon the parent fungus. That is to say, we may be doubtful whether in such a case their origin ought to be considered Homogenetic or Heterogenetic. It may be that many of the lower fungi are such changeable organisms, and so prone to respond to the various “conditions” acting upon them (which would be almost certainly the case if they had been developed from a _Bacterium_ in two or three days--the _Bacterium_ itself having been evolved _de novo_) that no very valid distinction can here be drawn between Homogenesis and Heterogenesis. Our whole point of view, in fact, concerning such fungi as are seen to develop through _Leptothrix_ forms from _Bacteria_ must be entirely altered, if it is once conceded that _Bacteria_ may arise _de novo_. Such simple _Mucedineæ_ would then have to be regarded as mere upstart organisms only a few removes from dead matter, and--in view of the greater molecular mobility of living matter--capable of being modified in shape and form even more than the most changeable crystals under the influence of altering “conditions.” We should have no longer to do with the members of a stable species, which had been reproducing its like through countless geologic ages anterior to the advent of man upon the earth. Indeed, in order to reconcile such a possibility with the seemingly contradictory fact of the known extreme changeability of these lower forms of life, we hear only vague hints thrown out about our imperfect knowledge of the “limits within which species may vary.” As if, in the face of what we do know concerning hereditary transmission, this changeability did not make it almost impossible to conceive that there should have been an unbroken series of such organisms since that remote epoch of the earth’s history, when the first organisms of the kind made their appearance. It does not seem to me that the presumed permanence of a very changeable organism is consistent with, or rendered more explicable by, the supposition that _some_ representatives of the species _have_ constantly been undergoing progressive modifications which have been successively perpetuated by inheritance, in the shape of distinct specific forms. Why should some be presumed to have undergone so much change, whilst others (presenting an equal and an extreme degree of modifiability, even to the present day) are supposed to have preserved the same specific form through a countless series of changing influences? 2. HETEROGENETIC MODE OF ORIGIN OF BACTERIA AND OF TORULÆ.