VARIATION UNDER NATURE 41 



nition above given of a true species. It should be added that De 

 Candolle no longer believes that species are immutable creations, 

 but concludes that the derivative theory is the most natural one, 

 "and. the most accordant with the known facts in palaeontology, 

 geographical botany, and zoology, of anatomical structure and 

 classification." 



When a young naturalist commences the study of a group of 

 organisms quite unknown to him, he is at first much perplexed in 

 determining what differences to consider as specific and what as 

 varietal; for he knows nothing of the amount and kind of varia- 

 tion to which the group is subject; and this shows, at least, how 

 very generally there is some variation. But if he confine his atten- 

 tion to one class within one country he will soon make up his mind 

 how to rank most of the doubtful forms. His general tendency will 

 be to make many species, for he will become impressed, just like 

 the pigeon or poultry fancier before alluded to, with the amount 

 of difference in the forms which he is continually studying; and 

 he has little general knowledge of analogical variation in other 

 groups and in other countries by which to correct his first impres- 

 sions. As he extends the range of his observations he will meet with 

 more cases of difficulty; for he will encounter a greater number of 

 closely allied forms. But if his observations be widely extended he 

 will in the end generally be able to make up his own mind; but he 

 will succeed in this at the expense of admitting much variation, 

 and the truth of this admission will often be disputed by other 

 naturalists. When he comes to study allied forms brought from 

 countries not now continuous, in which case he cannot hope to find 

 intermediate links, he will be compelled to trust almost entirely to 

 analogy, and his difficulties will rise to a climax. 



Certainly no clear line of demarcation has as yet been drawn 

 between species and sub-species — that is, the forms which in the 

 opinion of some naturalists come very near to, but do not quite 

 arrive at, the rank of species; or, again, between sub-species and 

 well-marked varieties, or between lesser varieties and individual 

 differences. These differences blend into each other by an insen- 

 sible series; and a series impresses the mind with the idea of an 

 actual passage. 



Hence I look at individual differences, though of small interest 

 to the systematist, as of the highest importance for us, as being 

 the first steps toward such slight varieties as are barely thought 

 worth recording in works on natural history. And I look at vari- 

 eties which are in any degree more distinct and permanent, as steps 

 toward more strongly marked and permanent varieties; and at the 



