438 Dr. V. Fatio on the Variability of the 



Several naturalists have already more or less studied and 

 described the series of transformations which, under the 

 influence of the variability of the conditions of existence, have 

 gradually modified, sometimes the actions, and sometimes the 

 forms of certain animals and plants, often sufficiently to 

 render unrecognizable the traits of relationship which ought 

 to unite individuals which, at the first glance, are completely 

 different. 



The particular point to which I desire here to call attention 

 will not, therefore, find its interpretation in an entirely new 

 order of ideas. However, as each new stone added to the 

 edifice of an opinion cannot fail to be of use, I think I ought 

 to take advantage of some of my most recent observations to 

 expound succinctly some reflections which have by little and 

 little grouped themselves in my mind since I have investigated 

 the Swiss Vertebrata and their variability under difierent con- 

 ditions. 



A conscientious zoologist can no longer establish new species 

 so easily as heretofore. Many apparently distinctive cha- 

 raters fall to the ground or lose more or less of their impor- 

 tance before a thorough study of possible modifications. Each 

 character calls for serious discussion ; it is necessary to seek, 

 if not the limits of variability, at least the points which, under 

 such or such an ensemble of appreciable conditions, seem to 

 be the most solid. 



It is, in fact, to the narrowness of the limit ascribed to 

 the species in the old definitions, and to the often inconside- 

 rate multiplication of specific types apparently different, 

 that we owe in a great degree the confusion which now reigns 

 either in certain parts of classification, or in the minds of 

 many people who seek, in different directions, the foundation 

 of truth. 



The species is very difficult to define or to limit ; for a group 

 of individuals similar to each other, exactly like a certain 

 individual, attributed to such or such a species, seems to be 

 nothing more in reality than the actual expression^ under cer- 

 tain given conditions^ of a form taken upon such or such a step 

 of the animal scale, or upon such or such a branch of a genea- 

 logical tree*. 



* The subject of which alone I wish to treat here is too restricted to 

 lead me to launch out now upon the hypotheses as to the derivation of 

 the original types. Science in general and pala^iontology in particular 

 cannot yet offer us any definitive solution of this question. I have nothing 

 to do, therefore, at present with the question whether there have been 

 several animal scales, oi: whether a single scale has been at first composed 



