HAECKEL: GENEALOGICAL TREES 251 



related organisms with one another and with the common 

 ancestral form " (ii., p. 420). 



The degree of systematic relationship is thus the degree 

 of genealogical affinity. It follows that the natural system 

 of classification may be converted straightway into a 

 genealogical tree, and this is actually what Haeckel does in 

 the General MorpJwlogy. The genealogical trees depicted in 

 the second volume (plates i.-viii.) are nothing more than 

 graphic representations of the ordinary systematic relation- 

 ships of organisms, with a few hypothetical ancestral groups 

 or forms thrown in to give the whole a genealogical turn. 



If the genealogical tree is truly represented by the 

 natural system, it would seem that for each genus a single 

 ancestral form must be postulated, for each group of genera 

 a single more primitive form, and so in general for each of 

 the higher classificatory categories, right up to the phylum. 

 Species of one genus must be descended from a generic 

 ancestral form, genera of one family from a single family 

 Urform, and so on for the higher categories. 



This consequence was explicitly recognised by Haeckel. 

 "Genera and families," he writes, "as the next highest 

 systematic grades, are extinct species which have resolved 

 themselves into a divergent bunch of forms (Formenbuschel) " 

 (ii., p. 420). 



The archetype of the genus, family, order, class and 

 phylum was thus conceived to have had at some past time 

 a real existence. 



The natural system of classification is based upon a 

 proper appreciation of the distinction between homological 

 -and analogical characters. Haeckel, following Darwin, 

 naturally interprets the former as due to inheritance, the 

 latter as due to adaptation, using these words, we may note, 

 in their accepted meaning and not in the abstract empty 

 sense he had previously attributed to them. 1 Similarly the 

 "type of organisation," in von Baer's sense, was due to 

 heredity, the "grade of differentiation " to adaptation. 



So far Haeckel merely emphasised what Darwin had 

 already said in the Origin of Species. But by his statement 

 of the " biogenetic law," and particularly by the clever use 

 1 But he himself would not admit this ! See Gen. Morph., ii., p. ii. 



