Of still greater, nay, the very greatest importance to the hypothesis of spontaneous generation are, finally, the exceedingly remarkable _Monera_, those creatures which we have already so frequently mentioned, and which are not only the simplest of all observed organisms, but even the simplest of all imaginable organisms. I have already described these wonderful “_organisms without organs_,” when examining the simplest phenomena of propagation and inheritance. We already know seven different genera of these Monera, some of which live in fresh water, others in the sea (compare above, p. 184; also Plate I. and its explanation in the Appendix). In a perfectly developed and freely motile state, they one and all present us with nothing but a simple little lump of an albuminous combination of carbon. The individual genera and species differ only a little in the manner of propagation and development, and in the way of taking nourishment. Through the discovery of these organisms, which are of the utmost importance, the supposition of a spontaneous generation loses most of its difficulties. For as all trace of organization—all distinction of heterogeneous parts—is still wanting in them, and as all the vital phenomena are performed by one and the same homogeneous and formless matter, we can easily imagine their origin by spontaneous generation. If this happens through _plasmogeny_, and if plasma capable of life already exists, it then only needs to individualize itself in the same way as the mother liquor of crystals individualizes itself in crystallization. If, on the other hand, the spontaneous generation of the Monera takes place by true _autogeny_, then it is further requisite that that plasma capable of life, that primæval mucus, should be formed out of simpler combinations of carbon. As we are now able artificially to produce, in our laboratories, combinations of carbon similar to this in the complexity of their constitution, there is absolutely no reason for supposing that there are not conditions in free nature also, in which such combinations could take place. Formerly, when the doctrine of spontaneous generation was advocated, it failed at once to obtain adherents on account of the composite structure of the simplest organisms then known. It is only since we have discovered the exceedingly important Monera, only since we have become acquainted in them with organisms not in any way built up of distinct organs, but which consist solely of a single chemical combination, and yet grow, nourish, and propagate themselves, that this great difficulty has been removed, and the hypothesis of spontaneous generation has gained a degree of probability which entitles it to fill up the gap existing between Kant’s cosmogony and Lamarck’s Theory of Descent. Even among the Monera at present known there is a species which probably, even now, always comes into existence by spontaneous generation. This is the wonderful _Bathybius Hæckelii_, discovered and