462 NOTES. 



a repetition of the same causes in the realm of or^^^anic nature is 

 simply impossible ; thus the twofold origination of one and the 

 same species from dillerent parent forms brought into existence 

 by dissimilar causes is physically inconceivable and hence impos- 

 sible. Granted. The error and logically false conclusion involved 

 in Haeckclism does not lie in this but in the presumption which 

 asserts that the forms or individuals which it declares to belong to the 

 same species must be identical. This they certainly are not, and 

 though zoologists may include them under the concept of a 'species ' 

 this is done on extremely various grounds that are without exception of 

 a subjective character. No one is competent to deliver an objective 

 decision as to whether these or those individuals actually constitute 

 only one, or two, or more species ; the criteria for such a determi- 

 nation are wholly wanting. Moreover, the monophyletic hypothesis 

 entirely ignores the fact that in by far the greater number of cases two 

 individuals are needed for the propagation of new individuals, and these, 

 irrespective of their sexual diiierences, certainly need not invariably 

 belong to the same species ; the possibility of hybridisation, i.e. the 

 fertile union of two individuals of different species, is fully established. 

 W'e know, moreover, that hybridisation is a favourite method employed 

 by Nature for the origination of new forms — perhaps, indeed, the most 

 powerful means at her command. Now, if the hybrid union of a 

 species, A, with three others, B, c, D, results in each case in an analogous 

 but different deviation from both parents, if this new character, com- 

 mon to the three families of hybrid progeny, A B, A c, and A D, justifies 

 us, according to ovr subjective views, in establishing a new genus, we 

 here have three different species of a second genus derived from the 

 three originally different species, B, c, D ; they have originated by a 

 polyphyletic process. The Amphioxus is one of the cosmopolitan 

 species, but the specimens from different localities exhibit some not 

 inconsiderable differences. Now, if new forms were to arise from these 

 dissimilar individuals, these might still possibly belong to one and 

 the same genus ; still, the Brazilian, the Philippine, the American, and 

 the Australian species of this new genus would not have originated 

 from a transformation of the descendants of a single pair, as the mono- 

 phyletic hypothesis requires. I can make this discussion quite in- 

 telligible simply by quoting the following lines from Darwin : ' I will 

 only remark,' he says, 'that if two species of two closely allied genera 

 produced a number of new and divergent species, I can believe that 

 these new forms might sometimes approach each other so closely that 

 they would for convenience' sake be classed in the same genus, and thus 

 two genera would converge into one.' Thus Darwin regards it as 

 possible that the species of one and the same genus may have 

 been derived from species not merely of one but of two different 

 genera. All the most careful and recent investigations make it seem 



