XI, C, 4 
Copeland: Natural Selection 
151 
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. Pag'e references not 
stated to be otherwise are to this paper. 
