NOTES. 46 1 



regards the principle of isolation of new forms and tlie hindering of in- 

 breeding with the parent form as an integral portion of his theory. I 

 will here quote the most striking examples. He says (in Animals under 

 Domestication, ch. xv.) : ' The prevention of free crossing and the 

 intentional matching of individual animals are the comer-stone of the 

 breeder's art. No man in his senses would expect to improve or 

 modify a breed in a particular manner or keep an old breed true and 

 distinct unless he separated his animals. The killing of inferior 

 animals in each generation comes to the same thing as their separation.' 

 The struggle for existence combined with other causes produces the 

 isolation which is indispensable to the phenomena of a race or species 

 by causing the necessary separation from the parent form and by hin- 

 dering its crossing with it again. Elsewhere Darwin says : ' A country 

 having species, genera, and whole families peculiar to it, will be the 

 necessary result of its having been isolated for a long period, sufficient 

 for many series of species to have been created on the type of pre- 

 existing ones.' 



JVote 113, pat/e 293. Gunther on the Tortoises of Mauritius and 

 Galscpagos, Anil. Mag. Jfat. Mist. 1874, vol. xiv. ; SilUman's Journal, 1874, 

 ser. 3, vol. viii. p. 403. These tortoises are also interesting from their 

 enormous size. Gunther comes to the conclusion that those of the 

 Mauritius and those of Galapagos must have originated independently. 



Note lli,page 294. The question whether similar forms can have a 

 polyphyletic origin (be derived, that is, from independent parent stocks) 

 or no, has gradually become the corner-stone of that extreme and 

 dogmatic form of Darwinism which in Germany has been designated 

 as Haecltelism.* Haeckel himself, the founder of this creed, allows of no 

 doubt that all those characters collectively of a species or of a genus 

 which present themselves to us as identical can only and uncondition- 

 ally, as being identical, have been derived from a single parent-stock. 

 This is known as Monojphyletic descent, and according to this view all 

 the species of a genus must have descended from one parent species, 

 all the genera of a family from one parent genus, and so forth. In 

 opposition to this is the view that apolyphyletio origin may be possible, 

 i.e. that the forms comprehended by us in a genus or a family may 

 have descended from more than one parent species or genus. 



The theoretical correctness of the monophyletic hypothesis may 

 be conceded unconditionally without any necessity for admitting its 

 practical correctness. Fundamentally the only correct view is that 

 any definite phenomenon must have had a definite cause, and that 



* Many of Haeckel's works are known to English readers through 

 excellent translations, as The Nat. Hist, of Creation,a.nd the Evolution of 

 Man (C. Kegan Paul & Co.). 



