104 Prof. Pictet on the Succession of Organised Beings 



the laws of physiologists, known under the names of the law of epi- 

 genesis or the law of symmetry, and many others, have no more 

 characters of necessity and certainty than the laws relating to the 

 succession of organised beings. Let us acquit palasontologists, there- 

 fore, of the blame that has been imputed to them of excessive bold- 

 ness in expressing the deductions they have drawn from the entire 

 view of observed facts. 



In discussing the question itself of the specialty of fossils, a great 

 difficulty meets us at the outset, namely the impossibility of defining 

 a species in an exact and sufficient manner. This difficulty is, per- 

 haps, one of the principal causes of the confusion which has too 

 much prevailed in the discussion of this law. In fact, w^e so little 

 know what constitutes a species, that the use of this word necessarily 

 entails some degree of vagueness and uncertainty. The definition 

 of Buffon, De Candolle, and Blumenbach, and in general all the 

 means proposed to throw light on the study of a species, have not 

 entirely dissipated the cloud which still rests on the idea. These 

 difficulties have even appeared sufficient to some naturalists to in- 

 duce them to deny the reality of a species altogether, and to consi- 

 der it a mere creation of the fancy. I cannot follow them this 

 length,^ and I believe that a species exists in nature, maintained 

 and preserved by indisputable physiological laws ; but as to fixing 

 its limits synthetically, or defining it precisely, this I consider almost 

 impossible in the present state of science. If we endeavour to give 

 an account of what a species is by analysis, the following appear to 

 me to be the only facts upon which we can proceed. 



Every organised being springs from parents, that is to say, from 

 one or two beings similar to itself. Whether it proceed from them 

 by simple separation, slip, stolon, bud, &c., or whether it be the re- 

 sult of true fecundation, the new being resembles that to which it 

 owes its existence, and without being altogether identical with it, 

 possesses all its essential characters. These characters, proper to the 

 family properly so called, that is to say, to the father, mother, and off- 

 spring, always form a whole which it is very easy to distinguish. If 

 the transmission of the characters always took place without modifi- 

 cation, it would be easy to understand and define a species, for the 

 direct comparison of two successive generations would resolve all 

 doubtful cases ; and the characters common to the family properly 

 so called, being the same in all the beings proceeding from the same 

 primitive couple, would always enable us to ascertain and establish 

 this common origin, which would thus become a solid and certain 

 basis for the species. 



But things are far from always proceeding in this way, and va- 

 rious circumstances modify these facts, so simple in their origin. 

 We remark, in the first place, individual varieties, that is to say, 

 slight modifications of size, colour, temperament, &c., which direct 

 generation does not always reproduce, and which increase in conse- 



