How, he asks, can they reappear?
Is it not more likely that these simple organisms are themselves regenerated?
After much verbiage and repetition, he concludes: "We may conceive that the simplest organisms can arise from a minute mass of substances which possess the following conditions--namely, which will have solid parts in a state nearest the fluid conditions, consequently having the greatest suppleness and only sufficient consistence to be susceptible of constituting the parts contained in it.

Such is the condition of the most gelatinous organized bodies.
"Through such a mass of substances the subtile and expansive fluids spread, and, always in motion in the milieu environing it, unceasingly penetrate it and likewise dissipate it, arranging while traversing this mass the internal disposition of its parts, and rendering it suitable to continually absorb and to exhale the other environing fluids which are able to penetrate into its interior, and which are susceptible of being contained.
"These other fluids, which are water charged with dissolved (_dissous_) gas, or with other tenuous substances, the atmospheric air, which contains water, etc., I call containable fluids, to distinguish them from subtile fluids, such as caloric, electricity, etc., which no known bodies are believed to contain.
"The containable fluids absorbed by the small gelatinous mass in question remain almost motionless in its different parts, because the non-containable subtile fluids which always penetrate there do not permit it.
"In this way the uncontainable fluids at first mark out the first traces of the simplest organization, and consequently the containable fluids by their movements and their other influences develop it, and with time and all the favorable circumstances complete it." This is certainly a sufficiently vague and unsatisfactory theory of spontaneous generation.

This sort of guess-work and hypothetical reasoning is not entirely confined to Lamarck's time.

Have we not, even a century later, examples among some of our biologists, and very eminent ones, of whole volumes of _a priori_ theorizing and reasoning, with scarcely a single new fact to serve as a foundation?
And yet this is an age of laboratories, of experimentations and of trained observers.

The best of us indulge in far-fetched hypotheses, such as pangenesis, panmixia, the existence of determinants, and if this be so should we not excuse Lamarck, who gave so many years to close observation in systematic botany and zooelogy, for his flights into the empyrean of subtle fluids, containable and uncontainable, and for his invocation of an _aura vitalis_, at a time when the world of demonstrated facts in modern biology was undiscovered and its existence unsuspected?
_The Preexistence of Germs and the Encasement Theory._--Lamarck did not believe in Bonnet's idea of the "preexistence of germs." He asks whether there is any foundation for the notion that germs "successively develop in generations, _i.e._ in the multiplication of individuals for the preservation of species," and says: "I am not inclined to believe it if this preexistence is taken in a general sense; but in limiting it to individuals in which the unfertilized embryos or germs are formed before generation.