We believe that the melting point of platinum and the freezing point of mercury are the same as they were a hundred years ago, and as they will be a hundred years hence. Now, carefully remember that so far as we can see at all, it must be so with life. Life inheres in protoplasm; but just as you cannot get _abstract matter_--that is, matter with no properties or modes of motion--so you cannot get _abstract_ protoplasm. Every piece of living protoplasm we see has a history; it is the inheritor of countless millions of years. Its properties have been determined by its history. It is the protoplasm of some definite form of life which has inherited its specific history. It can be no more false to that inheritance than an atom of oxygen can be false to its properties. All this, of course, within the lines of the great secular processes of the Darwinian laws; which, by the way, could not operate at all if caprice formed any part of the activities of nature. But let me give a practical instance of how what appears like fact may override philosophy, if an incident, or even a group of incidents, _per se_ are to control our judgment. Eighteen years ago I was paying much attention to vorticellae. I was observing with some pertinacity _Vorticella convallaria_; for one of the calices in a group under observation was in a strange and semi-encysted state, while the remainder were in full normal activity. I watched with great interest and care, and have in my folio still the drawings made at the time. The stalk carrying this individual calyx fell upon the branch of vegetable matter to which the vorticellan was attached, and the calyx became perfectly globular; and at length there emerged from it a small form with which, in this condition, I was quite unfamiliar; it was small, tortoise-like in form, and crept over the branch on setae or hair-like pedicels; but, carefully followed, I found it soon swam, and at length got the long neck-like appendage of _Amphileptus anser_! Here then was the cup or calyx of a definite vorticellan form changing into (?) an absolutely different infusorian, viz., _Amphileptus anser_! Now I simply reported the _fact_ to the Liverpool Microscopical Society, with no attempt at inference; but two years after I was able to explain the mystery, for, finding in the same pond both _V. convallaria_ and _A. anser_, I carefully watched their movements, and saw the _Amphileptus_ seize and struggle with a calyx of _convallaria_, and absolutely become encysted upon it, with the results that I had reported two years before.