only an evolution of the individual from the moment when it became more heterogeneous by the differentiation of parts and functions, but also an evolution of the ensemble of living beings, from the first appearance of life in its least differentiated form up to the highest degree of complexity in structure and function.
If life is an evolution, of what is it an evolution? If the question refers to an individual of any given species, the answer is easily given, for we can study the history of its life from the germinal cell to the period of its full development, and to the end of its life. But if the question refers to the ensemble of living Nature, only the middle portion of which is known to us, and the beginning of which we have no idea of save in imagination, then the reply must be only an hypothesis. We find groups differing from one another by their respective degrees of vital evolution, and we regard them as being, not as it were links of one chain, but rather the result of an evolution which has taken different directions owing to different circumstances. Hence we can admit only one starting-point, though the goals are many. The divergent lines which we find in the development of the forms of living things, in the history of life, warrant our supposing the starting-point to be one, and at this point the evolution hypothesis must place the formation of primordial organic matter, whose reactions with its environment present the first crude examples of vital function.
The hypothesis which accounts for the production of life by the spontaneous generation of a complete organism from simple protoplasm is irreconcilable with evolution; this would suppose something more than an evolution, in fact a beginning in the absolute sense, an enormous hiatus between the causes and their supposed effects. But on the theory of evolution we can conceive of another mode of formation. It is possible that even now, under existing cosmical conditions, organic matter is produced; but it is more probable that it was formed in an epoch when the cosmical forces now known to us, especially heat and light, had on earth a greater intensity than at present. The first types must have been more simple, less definite, less fixed in form and structure, than the lowest rhizopods of our day. Indeed, they must have been more nearly allied to protoplasm than even Haeckel's Protogenes; and, before evolution could derive from these types our present infusoria, ages and ages must have elapsed. Strictly speaking, we cannot call the first living thing an organism at all, in the true sense of that term; it is stretching the meaning of words to speak of types in connection with beings whose form must have been perfectly unstable, and whose organization had no structure.
Of this quasi-organism we have merely a symbolic conception, formed by combining two positive, empiric elements, viz., transformations of substances strictly evolutive, such as we see in the laboratory
