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SCIENCE. 



[N. S. Vol. III. No. 61. 



cover the series of organic forms which he 

 studies. He learns the difference between 

 its beginning and its ending. His natural 

 divisions are the steps or stages which sep- 

 arate the one extremity from the other. 

 The series may be greater or they may be 

 lesser, i. e., more or less comprehensive, 

 and it is to the series of different grades 

 that we give the different names of the 

 genus, family, order, etc. 



We know that the characters of specific 

 value in given cases are usually more 

 numerous than those of higher groups. We 

 know that they are matters of proportions, 

 dimensions, textvires, patterns, colors, etc., 

 which are many. The characters of the 

 higher groups, on the contrary, are what we 

 call structural, i. e., the presence, absence, 

 separation or fusion of elemental parts, as 

 estimated by a common morphologic stand- 

 ard ; and it is the business of the morph- 

 ologist to determine each case on this basis. 

 In these characters lies the key to the larger 

 evolution, that of the higher aggregations 

 of living things. On the contrary, the study 

 of the origin of species characters gives us 

 the evolution of species within the genus, 

 but nothing more, except by inference. 



Classification, then, is a record of charac- 

 ters, arranged according to their values. 

 There still lingers, in some quarters, a dif- 

 fei'ent opinion. This holds that there is 

 such a thing as a ' natural system,' as con- 

 trasted with ' an anatomical system.' Ex- 

 amination shows that the supporters of this 

 view suppose that there is some bond of 

 affinity between certain living beings which 

 is not expressed in anatomical characters. 

 A general resemblance apparent to the eye 

 is valued by them more highly than a struc- 

 tural character. If this 'general appear- 

 ance ' is analj'zed, however, it is found to 

 be simply an aggregate of chai-acters usu- 

 ally of the species type, which by no means 

 precludes the presence of anatomical differ- 

 ences. And these anatomical differences 



may indicate little relationship, in spite of 

 the general resemblance of the species con- 

 cerned, or thej' may have only the smallest 

 value attached to such characters, i. e., the 

 generic. It is with regard to the generic 

 characters that the chief difference of prac- 

 tice exists. But it is clear that the record 

 of this grade of characters cannot be modi- 

 fied by questions of specific characters. The 

 two questions are distinct. Both represent 

 nature, and must be formulated. In fact, 

 I have long since pointed out that the same 

 species, so far as species characters go, may 

 have different generic characters in different 

 regions. Also that allied species of different 

 genera may have more specific characters 

 in common than remote species of the same 

 genus. 



The anticipation naturally intrudes itself 

 that the characters which distinguish the 

 steps in a single evolutionary or genealogi- 

 cal line must disappear with discovery, and 

 new ones appear, and that they must be all 

 variable at certain geological periods, and 

 hence must become valueless as taxonomic 

 criteria. And it is therefore concluded that 

 our systematic edifice must lose precision 

 and becomes a shadow rather than a reality. 

 I think that as a matter of fact this will not 

 be the result, and for the following reasons: 

 In the first place, when, say all the generic 

 forms of a genealogical line, shall have been 

 discovered, we will find that each one of 

 them will differ from its neighbor in one 

 character only. This naturally follows from 

 the fact that two characters rarely, if ever, 

 appear and disappear contemporaneously. 

 Hence, generic characters will not be drawn 

 up so as to include several points. For a 

 while, there will be found to be combina- 

 tions of two or three characters which will 

 serve as definitions, but discovery will rele- 

 gate them to a genus each. Each of these 

 characters will be found to have what I 

 have called the ' expression point,' or the 

 moment of completeness, before which it 



