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 vorticellæ. 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 setæ 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.
And there can be no doubt but this is the key to the cases that come to us again and again of minute forms suddenly changing into forms wholly unlike. It is happily among the virtues of the man of science to "rejoice in the truth," even though it be found at his expense; and true workers, earnest seekers for nature's methods, in the obscurest fields of her action, will not murmur that this source of danger to younger microscopists has been pointed out, or recalled to them.
And now I bid you, as your president, farewell. It has been all pleasure to me to serve you. It has enlarged my friendships and my interests, and although my work has linked me with the society for many years, I have derived much profit from this more organic union with it; and it is a source of encouragement to me, and will, I am sure, be to you, that, after having done with simple pleasure what I could, I am to be succeeded in this place of honor by so distinguished a student of the phenomena of minute life as Dr. Hudson. I can but wish him as happy a tenure of office as mine has been.
Delivered by the Rev. Dr. Dallinger, F.R.S., at the annual meeting of the Royal Microscopical Society, Feb. 8, 1888.—Nature.