i6 The Science of Life. 



register of affinities, it was used to express the supposed 

 facts of descent. To Ernst Haeckel belongs the credit, 

 or, as some critics would say, the responsibility of intro- 

 ducing the use of genealogical trees in zoology and 

 botany. In his Generelle Morphologic (1866), and in his 

 Schopfungsgeschichte (gth edition, 1897), he displayed 

 numerous genealogical trees designed to show the 

 descent of various stocks and types of animals and 

 plants. 



There can be no doubt that in so doing he focussed 

 the idea of descent into vividness, and by the very 

 definiteness of the notation forced naturalists to a 

 criticism of the reality of the supposed lines of descent. 



Prof. L. von Graff says of Haeckel's Stammbaume> 

 " there is due to them the immortal credit of having 

 given the first impetus to the grand revolution in the 

 animal morphology of the last decades ". 



On the other hand, there are critics who maintain 

 that the method is fallacious. If we had a knowledge 

 of all forms that have lived, and a perfected classifi- 

 cation of all these forms, then the tree-notation would 

 be permissible. It would simply be another way of 

 stating the perfected classification. But such perfection 

 is unattainable. It is further urged, that while the 

 notation may be permissible to express degrees of affin- 

 ity, it has led by its symbolic suggestiveness to the 

 common error of regarding a series of affinities as 

 necessarily representing the actual line of descent. To 

 take an obvious case, the double-breathing mud-fishes 

 or Dipnoi are in many ways intermediate between fishes 

 and amphibians, and might be appropriately represented 

 in this position on a genealogical tree, yet it would be 

 a mistake to suppose that the Dipnoi were the real 

 ancestors of the Amphibia. But we cannot abandon a 

 vivid notation simply because the careless read more 

 into it than it is meant to express. 



In justice to Haeckel, a single sentence may be 

 quoted: "Of course this genealogical tree, which re- 

 presents the natural classification (system) of organisms, 

 can never be drawn with absolute certainty, but always 

 only in approximation thereto ". 



