OF SPECIES 37 



shapes of individuals, perpetuated by reproduction or generation. 

 Such are a great number of these alleged species that we see every day. 



Meanwhile, the farther we advance in our knowledge of the various 

 organised bodies which cover almost every part of the earth's surface, 

 the greater becomes our difficulty in determining what should be 

 regarded as a species, and still more in finding the boundaries and 

 distinctions of genera. 



According as the productions of nature are collected and our 

 museums grow richer, we see nearly all the gaps filled up and the lines 

 of demarcation effaced. We find ourselves reduced to an arbitrary 

 decision which sometimes leads us to take the smallest differences 

 of varieties and erect them into what we call species, and sometimes 

 leads us to describe as a variety of some species shghtly differing 

 individuals which others regard as constituting a separate species. 



Let me repeat that the richer our collections grow, the more proofs 

 do we find that everjrthing is more or less merged into everything 

 else, that noticeable differences disappear, and that nature usually 

 leaves us nothing but minute, nay puerile, details on which to found 

 our distinctions. 



How many genera there are both among animals and plants, among 

 which the number of species referred to them is so great that the study 

 and determination of these species are well nigh impracticable ! The 

 species of these genera, arranged in series according to their natural 

 affinities, exhibit such sHght differences from those next them as to 

 coalesce with them. These species merge more or less into one another, 

 so that there is no means of stating the small differences that dis- 

 tinguish them. 



It is only those who have long and diUgently studied the question 

 of species, and who have examined rich collections, that are in a 

 position to know to what extent species among living bodies merge 

 into one another. And no one else can know that species only appear 

 to be isolated, because others are lacking which are close to them 

 but have not yet been collected. 



I do not mean that existing animals form a very simple series, 

 regularly graded throughout ; but I do mean that they form a branch- 

 ing series, irregularly graded and free from discontinuity, or at least 

 once free from it. For it is alleged that there is now occasional dis- 

 continuity, owing to some species having been lost. It follows that 

 the species terminating each branch of the general series are connected 

 on one side at least with other neighbouring species which merge into 

 them. This I am now able to prove by means of well-known facts. 



I require no hypothesis or supposition ; I call all observing 

 naturalists to witness. 



