110 FOURTH REPORT — 1834. 



parts upon the whole. Thus, for instance, respiration is neces- 

 sary to the heart's action, the heart's action to the respiratory 

 process ; neither can proceed after destruction of the nervous 

 system, and this requires for the production of its energy a due 

 supply of aerated blood. But this mutual relation of all and 

 each, alternately as cause and effect, has been improperly as- 

 sumed as a distinctive character of life. " The same is true of 

 an automaton, in which the moving power is part of the thing 

 moved : the same is also true of the planetary system as far as 

 we are acquainted with it*." 



Thus does the vital power, manifesting itself in the assimila- 

 tive process, occasion all the forms of life upon the earth. 

 Each living thing, according to the nature of that original power 

 (of which we can know nothing but by its effects), requires its 

 own modifications of the common conditions of life, and presents 

 an organization (upon which classification is based,) adapted to 

 the region and the element in which it is destined to exist. Of 

 these creatures, all that are not microscopic are observed to 

 proceed from parents similar in structure to themselves by modes 

 of propagation peculiar to the kind ; so that no one species, 

 under any modification of external condition, has ever been 

 known to assume the character or form which is distinctive of 

 another. The consideration of the stratification of the earth 

 assures us that all the families, genera, and species did not 

 commence their existence at one and the same epoch. On the 

 contrary, in the older strata are buried the remains of the sim- 

 pler forms of life alone ; in the more recent those of more com- 

 plex organization ; whilst the remains of the most perfect and 

 of man have not been discovered in the most recent stratum. 

 Of the remains which have thus been brought to light, some 

 belong to species and genera which still exist, others to such as 

 are lost. Some physiologists, taking their stand upon the 

 general fact of this successive advance towards perfection of 

 development in correspondence with the successive changes of 

 the globe, have concluded that all the various modifications 

 of life may be but successive metamorphoses of the first most 

 simple form. 



The undoubted fact that existing species have been perpe- 

 tuated unchanged for several thousands of years, would have 

 rendered such an opinion in the highest degree impi-obable, but 

 for the observations relative to the apparently spontaneous pro- 

 duction of animals and of plants from ©rganic matter in solution 

 — the apparent changes of species fi-om simpler to more complex 

 vmder favourable external circumstances — and the interchange of 



• Treviramis, Erscheimtngen vnd Gesetxe des oryanhchen Lehens. 



