ORIGIN OF THE SPECIFIC TYPE 303 



each other, which do not break off, but are all capable of life at the 

 same time, and so exist simultaneously on dilFerent areas ; they are 

 species adapted to different localities, not to different times. The 

 same is true of the snails of other isolated regions, except that the 

 chains of forms are usually not simple, but split up into several 

 chains of forms arising from one ancestral form, and under certain 

 circumstances each of these may break up into two or more diverging 

 series. The great number of related species in Madeira, or in the 

 Sandwich Islands, compels us to this assumption, although the branch- 

 ing of the genealogical trees can no longer be demonstrated with 

 certainty. 



This splitting up of forms into several series on a varied insular 

 region shows us once more that it is germinal selection alone which 

 forms the basis of all transformations, and that there is not, as earlier 

 naturalists, especially the botanists Nageli and Askenasy, maintained, 

 any peculiar impelling Force of Development innate in organisms. 

 If there were such a force, a species would be obliged to go on continu- 

 ously in the same direction, exactly like the Sarasins' chains of forms, 

 but no breaking of the species into one or many forms could occur. 

 But this breaking up into series is easy to understand when we take 

 germinal selection into consideration, for the germ-plasm contains 

 many ids and determinants, and each of these can enter upon new 

 variations, so that one colony can vary in this direction, another in 

 that, and a great diversity of forms living in isolation must, or at 

 least may be the result, as we see in the case of the Sandwich Islands. 



Let us delay a moment over the Sarasins' case of the Celebes 

 snails. We are dealing here with series of forms in regard to which 

 the ordinary conception of species fails us, for they contain varieties 

 whose extremes are as far apart as distinct species usually are, which 

 are not, however, distinct, since they are connected with one another 

 by one and often by several transition forms. Thus we can only 

 break them up into two or more ' species ' by an arbitrary division 

 at one place or other. The phenomenon itself is not new to us ; we 

 have seen that even Lamarck and Treviranus made use of similar 

 series of forms, connected by transition stages, in their attack upon 

 the old theory of creation, and sought to prove by means of these 

 that the idea of species is an artificial one, read into nature by man, 

 and not innate in nature, and that the forms of life were only 

 apparently fixed and sharply defined, being in reality in process of 

 slow transformation. Such beautiful and convincing examples as we 

 now possess were not available at that time, but it might even then be 

 said that it Avas the easier to make a new species the fewer examples 



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