234 LAMARCK AND DARWIN 



of Species (ist ed., 1859). A good part of this chapter is 

 given up to a discussion of the principles of classification, 

 only a few pages dealing with morphology proper. But, as 

 Darwin rightly saw, the two things are inseparable. 



We note first that there is no hint of the " scale of 

 beings " Darwin conceives the genealogical tree as many 

 branched. Animals can be classed in " groups under groups," 

 and cannot be arranged in one single series. 



He discusses first what kind of characters have the 

 greatest classificatory value. Certain empirical rules have 

 been recognised, more or less consciously, by systematists 

 that analogical characters are less valuable than homological, 

 that characters of great physiological importance are not 

 always valuable for classificatory purposes, that rudimentary 

 organs are often very useful, and so on. He finds that as 

 a general rule " the less any part of the organisation is 

 concerned with special habits, the more important it becomes 

 for classification" (p. 414), and adduces in support Owen's 

 remark that the generative organs afford very clear indica- 

 tions of affinities, since they are unlikely to be modified by 

 special habits. These rules of classification can be explained 

 " on the view that the natural system is founded on descent 

 with modification ; that the characters which naturalists con- 

 sider as showing true affinity . . . are those which have been 

 inherited from a common parent, and, in so far, all true 

 classification is genealogical ; that community of descent is 

 the hidden bond which naturalists have been unconsciously 

 seeking, and not some unknown plan of creation, or the 

 enunciation of general propositions, and the mere putting 

 together and separating objects more or less alike" (p. 420). 



In general, then, homological characters are more 

 valuable for classificatory purposes because they have a 

 longer pedigree than analogical characters, which represent 

 recent acquirements of the race. 



Coming to morphology proper, Darwin takes up the 

 question of the unity of type, and the homology of parts, for 

 which the unity of type is but a general expression. 



He treats this on the same lines as E. Geoffrey St 

 Ililaire, and Owen, referring indeed specifically to Geoffrey's 

 law of connections. " What can be more curious," he asks, 



