

THE KEVOLUTIONS OF THE CRUST OF THE EARTH. 315 



information. It is more discussed than any other in science, but as 

 yet with no definite result. 



Not only the origin of organized beings, but also their generic devel- 

 opment is difficult to explain. Some savans believe in the transforma- 

 tion of species ; others attribute to a direct creative force the continuous 

 succession of new organic forms. We may say with G. Bronn* that 

 we know of no natural force which can produce new species, and we do 

 not know the conditions which are necessary for their production. We 

 do not know any substance in which this force may be inherent; we 

 know only that the individuals of a species already in existence are 

 propagated by processes in accord with the simplicity or complication 

 of their organization. According to Isidore Geoffrey Saint- Hilairet 

 the two hypotheses mentioned are equally inadmissible in the sense and 

 to the extent they are ordinarily taken. They should not be entirely 

 rejected, freed from serious errors which are mingled with great and 

 fundamental truths. For instance, the fact given us by Professor 

 Agassiz is very remarkable, that ancient animals resemble the embryos 

 of the present existing animals of the same class, so that the geologi- 

 cal succession of extinct forms is parallel to the embryonic develop- 

 ment of recent animals.t The fact is undeniable, comparative anatomy 

 has expressed itself positively upon this subject, but what conclusion 

 can we draw from it ? This, perhaps : that the superior animals are de- 

 rived in a direct line from the animals whose forms are indicated by 

 the various stages of development of the embryo, or, going further 

 back to the egg, that the origin of all beings is in the infusoria. We do 

 not place much value upon such conclusions, for although, according to 

 M. Chevreul, the mutability of species is not an absurdity, to admit 

 it as a fact, and to draw consequences from it, is to abandon the experi- 

 mental system which does not permit us to use as a principle mere con- 

 jecture^ 



The character of species has been equally a subject of controversy 

 Certain physiologists base their determinations upon an indefinite 

 fecundity, others upon a common origin and upon resemblance. The 

 solution of these questions is not, however, absolutely indispeusabje for 

 the study of the organisms which have successively occupied the sur- 

 face of the globe, and for a sketch of the primitive world it is not 

 necessary first to settle whether each species is the product of a direct 

 creative force or the offspring of an extinct species. But it is essential 

 to know that no new organism manifests itself until all the conditions 

 of its existence are realized, which proves the influence of exterior cir- 

 cumstances upon the succession of organized beings. 



The development of plants is more directly dependent upon the nature 



"Handbuch einer Geschkhte der Xatur, t. ii, p. 653. 

 t Histoire Nat. Gau'r. dcs Elgncs Organ., t. i, p. 11. 

 t D'Archi.ic, Cours de FaUont. Strut., t. ii, p. 'J7 

 5 Journ. dcs Savants, 1840, p. 715. 



