440 Dr. V. Fatio on the Variability of the 



urge it towards constant variability. There seems to exist a law 

 of hereditary ■o^esemhlance which tends always to keep to the 

 specific ty])e^ and a law of variability by adaptation^ destined^ 

 on the contrary^ to modify every organism with the object of 

 fitting it to neio conditions of existence. 



Differences and variations of medium being incontestable, it 

 is irrational to try to prove the stability of the species by 

 closing our eyes to one whole side of the question, citing only 

 those cases in which the first of the above laws has gained 

 the victory, either directly or by return or atavism. In the 

 study of the variation of the species, in order to be impartial, 

 we must, I think, commence by fully recognizing the importance 

 of the first of the two opposing laws, and freely accepting it, 

 from the first, as a sort of h-ake preimposed upon future modi- 

 fications. 



While attributing great variability to the species, we must 

 not, however, I think, refuse proper names to all the more or 

 less different forms of creatures in various classes. Natural 

 history and classification have need of these distinctive desig- 

 nations, which become, as it w^ere, so many heads of chap- 

 ters and cadres for observations. INow-a-days, indeed, 

 there are many distinguished naturalists who see no incon- 

 venience in complicating the binary nomenclature by the 

 creation of a special name for each variety. The accumula- 

 tion of names is not, in fact, dangerous, if we always take 

 care to indicate the relations or affinities which bind together 

 two forms nominally separated. 



It has been said that it is the richest genera which furnish 

 the greatest amount of examples of variation by adaptation ; 

 this observation would, I think, be better represented by the 

 very simple remark that it is the largest genera which include 

 tlie most false species founded upon local varieties. 



I have often been struck with finding in several large 

 genera a species at once much more widely distributed, and 

 much more subject to vaiy, than the others, even in a very 

 restricted space. The red frog, in the genus Bana, and the 

 common toad in the genus Bufo, among the Batrachia, as 

 well as the trout in the genus Salmo, and the roach in the 

 genus Leuciscus, among fishes, may, among others, furnish 

 us with striking examples of cases of this kind. 



Such species, a sort of predominant branches, must be re- 

 garded as the parents or stocks of severed other so-called species, 

 more or less deviated, in different directions and in different 

 countries ; they are the type and, as it were, the centre of a 

 natural group of forms, all of which resemble them in different 

 degrees. 



