E VIDENCES OF E VOL UTION. 109 



which are revealed only by dissection likenesses 

 which can be fully appreciated only by the trained 

 anatomist. 



The more closely, then, one examines the divers 

 forms of life, the stronger grows the conviction that 

 they are genetically related in the manner indicated 

 by a Stammbaum, or genealogical tree. No other 

 system is competent to explain the facts observed ; 

 neither is there any other system which can explain 

 the " progressive shading off of characters common 

 to larger groups into more and more specialized 

 characters distinctive only of smaller and smaller 

 groups." It is just such a system as we should ex- 

 pect to find if the theory of descent be true ; just 

 such a system as would obtain if the law of parsi- 

 mony be admitted, the law, to-wit, that " forbids us 

 to assume the operation of higher causes when lower 

 ones are found sufficient to explain the observed 

 effects." Indeed, so powerful does the argument from 

 classification appear to some minds, that it alone is 

 regarded as decisive in favor of Evolution. Referring 

 to this matter Mr. Fiske declares: " In my own case 

 the facts presented in Agassiz' ' Essay on Classifica- 

 tion ' went far toward producing conviction before 

 the publication of Mr. Darwin's work on the ' Origin 

 of Species,' where the significance of such facts is 

 clearly pointed out and strongly insisted upon." ' 



The Argument from Structure and Morphology. 



We now pass to the argument from structure 

 and morphology. To confine ourselves to the ver- 



111 Cosmic Philosophy," vol. I, p. 454. 



