But there is a moral, as well as an intellectual demand, for thoroughness in recognizing the continuity of events. The scientific spirit can not excuse a covering up of past failures, as the formulating of verified results must imply testimony concerning them. It is of the very nature of religious conviction that we should learn from the failures of the past, and should advance out of them with higher wisdom. By common consent, therefore, we can have no accurate survey of the present situation, without making account of what has been recently passed, as well as what may be regarded as pressing upon our notice in these days. We do not need to travel a long way to the rear in order to discover how far astray we may be, both in expectations and in apprehensions; how readily we may get into confusion as to the interests involved in exciting controversies; and how much we need caution, making allowance for our partial survey of facts, and our uncertainty as to what may open up. By way of illustration, I shall refer to the history of discussions concerning so-called "_spontaneous generation_," mixed up with ascertained facts as to protoplasm, bathybius, or "living slime," as it has been called, and bacterium. The question eagerly discussed was whether there might be origin of life, without development from germ, seed, or ovum. The problem was one of those suggestions apt to arise under pressure of new conjectures and theories. While the scientific world was astir on the question of development, attention was turned for a time towards the possibility of a fresh beginning of organic forms, life which should be no development, but should rather seem as an uncaused existence,--"spontaneous generation." It might have been urged that the suggestion was contrary to reason; that "inexorable logic," of which we often hear from scientific observers, forbade the supposition; that all the conditions of scientific thought were against it; that the very conception of "spontaneous generation" was a logical inconsistency, alien to the requirements of scientific thought, as implying uncaused existence; but we were reminded that we are prohibited from supposing any thing is impossible in the pathway of science, that observation must be first, and reason only second, and accordingly the needful experiments went on under all due precautions. The brief chapter in the history of science which records expectations and results connected with these experiments, well deserves to be remembered. It is here selected for illustration, both on account of its inherent importance, and its relation to the theory of development, which must afterwards have special attention.