442 Dr. V. Fatio on the Variability of the 



rent as to have passed hitherto for two perfectly distinct species 

 in the eyes of most ichthyologists. It is well known that 

 the size of the basin and the relative abundance of alimenta- 

 tion have much influence on the dimensions of the animal. 

 The little brook-trout, which most zoologists still distinguish 

 under the name of Salar Ausonii (on the ground of its small 

 size,its thickset form, the shortness of its nose, the comparatively 

 larger dimensions of its eye, and some peculiarities in its den- 

 tition), is, in fact, in ray opinion, nothing more than a form of 

 the great trout of our lakes, which is called, according to cir- 

 cumstances, Trutta lacustris, T. Schiffermullerij Fario Mar- 

 siglii^ or Salmo lemanus. Most of the characters proposed for 

 its distinction are those of the early age of the fish. In a 

 small stream the trout, which cannot grow for want of room, 

 arrives at an advanced age retaining more or less the charac- 

 ters of infancy. It would be still more surprising to meet 

 with trout of 30 lb. in a few inches of water. Moreover I 

 have already remarked several times that the fishes — such as 

 the perch [Ferca Jluviatilis) and the chub {Squalius cephalus) , 

 for example — which inhabit the cold and poor waters of some 

 of our small elevated lakes in the Alps, also usually retain 

 several of the characteristic features of youth, their size also 

 being small. 



Many naturalists, misunderstanding the natural affinities 

 which bring together allied species, although at present per- 

 haps separated by very important geographical boundaries, 

 have gone so far ^s completely to deny the production of 

 races in organisms in a free state. Faivre, among others, 

 following Godron, unhesitatingly maintains that variations 

 and races are very rare among plants and animals in a wild 

 state. This author appears to me, in particular, to place him- 

 self in flagrant contradiction to direct observation when he 

 says, for example, " The races found under these conditions 

 are exceptional, to such an extent that many naturalists do 

 not hesitate to call in question their existence." 



Wallace, holding an exactly opposite opinion, published in 

 1858 a very interesting memoir on the tendency of varieties 

 to depart indefinitely from the original type. Trautschold 

 also, in 1861, drew a somewhat dift'erent conclusion from ana- 

 logous observations : according to the latter, " The varieties 

 which unite two species have also the power of modifying 

 themselves in more than two directions ; but the result ob- 

 tained by the changes effected in a third direction must not be 

 regarded as a simple variety, it must take rank as a new 

 species." The first author perhaps exaggerates, while the 

 second may seem to wish to specify a little too much ; how- 



