Chap. 



II. 



Doubtful Species. 



4i 



visional species, that is, are not known strictly to fulfil the defi- 

 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 paleontology, geo- 

 aphical botany and zoology, of anatomical structure and classifi- 



er; 



cation. 



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 variation 

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

 generally there is some variation. But if he confine his attention 

 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 dif- 

 ferences. These differences blend into each other by an insensible 

 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 towards such slight varieties as are barely thought worth 

 recording in works on natural history. And I look at varieties 

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



