108 Prof. Pictet on the Succession of Organised Beings 



fuse to acknowledge that we have here an hypothesis (very likely to 

 be true) which admits of the qualification of being open to dispute. 



It is by this combination of facts and hypotheses that we have 

 succeeded in establishing that beings which have a common origin 

 always preserve the traces of it, Ist^ by their power of reproduction, 

 and giving birth to fertile descendants ; 2d, by their tendency to re- 

 sume typical forms when they have lost them ; 3c?, by the identity 

 of their essential characters. An assemblage of beings thence ascer- 

 tained to have had a common origin, has been considered as consti- 

 tuting a species. In order to attain to this notion, we have been 

 obliged to associate the union of these characters with the necessity 

 of a common origin, and their absence with that of a diflferent ori- 

 gin. This association has been made by means of a bond of con- 

 nexion very likely to be true, and justifiable by sound arguments, 

 but which, in strict logic, must be regarded as hypothetical and open 

 to discussion. 



But i^ a species, regarded in a theoretical manner, is not, in the 

 present state of the science, capable of receiving a precise definition, 

 and of being placed on an unquestionable footing, it is not less true, 

 that, in practice, this word represents a very distinct idea. With- 

 out going back into the night of time, or pronouncing on the first 

 origin of beings, we can, by confining ourselves to the study of ac- 

 tual phenomena, characterise a species in such a manner that almost 

 all naturalists will be nearly agreed as to limits. Even such of them 

 as are most at variance in their theoretical opinions on this difficult 

 subject, are found, in general, to agree when they have occasion to 

 name and describe the beings which now people the world; and they 

 generally separate, as species, those beings which differ in more im- 

 portant characters than the modifications which external agents can 

 effect in their organism in the 'present day. The practical distinc- 

 tion of species rests almost wholly on the intelligent study of these 

 modifications. 



If the analysis I have given be correct, we may deduce three 

 consequences from it : 1st, That we do not always possess certain 

 means of determining whether beings have had a common origin ; 

 2d, That the limitation of actual species must remain independent 

 of the opinion which may be adopted as to their first origin ; 3c?, 

 That, in order to discover the law of specialty of fossils, we need 

 not take the connexion of the idea of a species with that of a com- 

 mon origin as the point of departure, but, on the contrary, set out 

 with the same principles as those which direct the study of existing 

 nature. This is the only means of preserving the necessary strict- 

 ness and precision in this discussion, for, unless we do so, we aban- 

 don a notion comprehended by every one, for an hypothesis which we 

 have seen to be open to discussion and dispute. 



This manner of adjusting the discussion on the specialty of fossils, 

 which renders it independent of the opinion that may be entertained 



