Genus, Species, Varieties 65 



corn " or maize type of plant, there are several hundred dif- 

 ferent kinds or varieties that are properly included under 

 the name, even if we use the " scientific name " — 2.ea 

 (genus) 7itays (species) . 



Sometimes the distinction is made between species and 

 varieties, and this distinction is often helpful. It does not, 

 however, relieve us of the difficulty of saying just exactly 

 what we mean by a species, or of saying just what is included 

 by any given " kind " of plant or animal. In thousands of 

 cases that have been carefully studied varieties ^nerge into 

 one another^ and species 7nerge into one another. So much 

 has this been the case wherever enough study has been ap- 

 plied to any group that those who know most about any 

 family of plants or animals are disposed to conclude that 

 the species as such does not exist as a definite fact of nature. 

 We know as facts only particular individuals, and we group 

 together under one name all the individuals that resemble 

 each other sufficiently to be conveniently considered by us 

 as a unity. Our own convenience or our own skill in dis- 

 criminating among similar individuals comes at last to be 

 the only test. For some purposes we are satisfied to take 

 more general resemblances into account, as when we speak 

 of " all animals " or of " all backboned animals," or of '' all 

 birds." 



It should not be necessary to observe, each time some 

 such collective expression is used, that nobody can possibly 

 know the whole group which the name is supposed to in- 

 clude. That seems to be common sense. We need still to be 

 reminded, however, that such, names do not stand for con- 

 crete realities, like " the friend of Androcles " or " the 

 Charter Oak." They stand for abstract ideas of " species " 

 or whole classes which, from the nature of our world 

 and from our own natural limitations, xue can never grasp 

 as facts (Fig. 12). 



Our own experience tells us that, although no two cats 

 may be alike, all cats are enough alike to be classed as cats 

 and to be distinguished from leopards, let us say, or tigers. 



