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these other engines represent a multiplied absorption of energy as the effects of the energy received by the parent engine, and may in time be supposed to reproduce themselves.  Further, we may suppose the parent engine to be small and capable of developing very little power, but the whole series as increasing in power at each generation.  Thus the primary energy relations of the vegetable organism are represented in these engines, and no violation of the second law of thermodynamics involved.

We might extend the analogy, and assuming these engines to spend a portion of their surplus energy in doing work against chemical forces—­as, for example, by decomposing water through the intervention of a dynamo—­suppose them to lay up in this way a store of potential energy capable of heating the boilers of a second order of engines, representing the graminivorous animal.  It is obvious without proceeding to a tertiary or carnivorous order, that the condition of energy in the animal world may be supposed fulfilled in these successive series of engines, and no violation of the principles governing the actions going on in our machines assumed.  Organisms evolving on similar principles would experience loss at every transfer.  Thus only a portion of the radiant energy absorbed by the leaf would be expended in actual work, chemical and gravitational, etc.  It is very certain that this is, in fact, what takes place.

It is, perhaps, worth passing observation that, from the nutritive dependence of the animal upon the vegetable,

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and the fact that a conversion of the energy of the one to the purposes of the other cannot occur without loss, the mean energy absorbed daily by the vegetable for the purpose of growth must greatly exceed that used in animal growth; so that the chemical potential energy of vegetation upon the earth is much greater than the energy of all kinds represented in the animal configurations.[1] It appears, too, that in the power possessed by the vegetable of remaining comparatively inactive, of surviving hard times by the expenditure and absorption of but little, the vegetable constitutes a veritable reservoir for the uniform supply of the more unstable and active animal.

Finally, on the question of the manner of origin of organic systems, it is to be observed that, while the life of the present is very surely the survival of the fittest of the tendencies and chances of the past, yet, in the initiation of the organised world, a single chance may have decided a whole course of events:  for, once originated, its own law secures its increase, although within the new order of actions, the law of the fittest must assert itself.  That such a progressive material system as an organism was possible, and at some remote period was initiated, is matter of knowledge; whether or not the initiatory living configuration was rare and fortuitous, or the probable result of the general action of physical laws acting among innumerable chances, must remain matter of