xi, c. 4 Copeland: Natural Selection \5\ 



are parts of one unbroken series." The distinction between 

 genus and species is certainly artificial. So, likewise, is any 

 attempt to frame a definition of a species by which one may 

 decide what differences are specific, what are varietal, what are 

 Jordanian, and, without prolonged study, what are merely inci- 

 dental and not hereditary at all. There is no way of distinguish- 

 ing between big and little specific differences nor between big 

 and little differences that are not specific. Certainly, we may 

 affirm that some differences are big and some others are little; 

 but, between the big and the little ones, nature presents an 

 absolutely continuous series of intermediate differences, which 

 we can surely find, if it is worth our while and we exercise 

 sufficient patience. 



In the recent paper which most completely summarizes his 

 views, 3 and which presents facts and methods of presentation 

 of such value that they deserve careful attention, Doctor Willis 

 places in apparent opposition to the theory of natural selection, 

 the theory that the commonness of species and the distribution 

 of species is a function of their age. 



In the Flora of Ceylon by Trimen and Hooker are notes by 

 Trimen indicating the commonness or distribution of all Angio- 

 sperms, except Gramineae (for which family Doctor Willis has 

 himself made these notes), by classification into six groups, 

 which in their order are Very Common (VC), Common (C), 

 Rather Common (RC), Rather Rare (RR), Rare (R), and Very 

 Rare (VR). "Very Rare" means very local, and, on the whole, 

 the classification refers more to distribution than to local abun- 

 dance. Doctor Willis has extracted and tabulated these notes 

 on distribution, in connection with the preparation of his Revised 

 Catalogue of the Indigenous Flowering Plants and Ferns of 

 Ceylon, and the analysis of all these statements is presented 

 with consummate clearness in a series of tables. 



In making these analyses, he has classified the indigenous 

 plants of Ceylon under three heads: First: Endemic species; 

 second: Species confined to Ceylon and Peninsular India; and 

 third: Species of wider distribution. His tables show conclu- 

 sively (p. 311) that: 



"In general the rarest plants in Ceylon are the local endemics, and 

 the commonest those of wide distribution. This is not at all the result 

 that one would expect had the endemics, as is usually supposed, been 

 developed by the aid of natural selection to suit the local conditions." From 



3 Phil. Trans. Roy. Soc. B. 206 (1915) 307-342. Page references not 

 stated to be otherwise are to this paper. 



