Professor Pictet on the Distribution of Fosnils, 259 



gether facts which admit of comparison,* and the limits of 

 species will acquire to his view a distinctness which does not 

 exist if we admit that they may vary in a way which cannot 

 be specified, and under the influence of causes which elude 

 examination, inasmuch as they are supposed to be different 

 from those which operate in our own day. 



The category of subanalogous species does not appear to 

 tne to be better established than that of the analogous species ; 

 for when M. Defrance gives this name to shells which differ 

 in characters too important to admit of their being referred 

 to the same species, it is evident that, in the present case, 

 the word is synonymous with different species or extinct 

 species. 



I am, therefore, of opinion, that it is more convenient and 

 consistent with facts, not to take into account, in this place, 

 the intermediate degrees of analogy ; and, in discussing the 

 law of the specialty of fossils, to apply to these remains of 

 ancient animals the same laws which guide naturalists in 

 establishing species in the actually existing state of the world. 

 M. Defrance' s distinctions will be of use in another respect, 

 in the comparison of the lost species of different geological 



* These rigorous principles will not prevent all subsequent discussion 

 on the prolonged influence of exterior agents ; I am even of opinion 

 that the partizans of the theory of the transition of species into each 

 other, ought necessarily to admit this starting-point. They have, in 

 fact, only two logical modes of proceeding ; either to limit, as we have 

 done, fossil species by the same principles which regulate the study of 

 living beings, or to unite in the same species all the animals which they 

 consider as having emanated from the same tj^pe. Now, if we admit this 

 latter mode of viewing the question, we shall fall into a very trouble- 

 some variability as to the limits of a species. Some naturalists would 

 unite only some animals, which appear to them to present too strong 

 resemblances to suppose for them a diiferent origin. Others, adopt- 

 ing the theories of gradual development in a more complete manner, 

 may associate, under the name of species, genera, and even entire 

 families, which they may regard as only a series of modifications of a 

 single primitive type. There would be no longer any fixed or uniform 

 rule. I am well aware that these extreme results are far from the 

 opinion of the skilful conchologist whose views I am opposing ; but we 

 must not take even a first step in a wrong path, for we shall be forced 

 to traverse it throughout. 



