246 THE PHILOSOPHY OF BIOLOGY 



the body of her husband, so He may have formed the 

 auditory ossicles of the higher vertebrate from those 

 parts of the visceral arches of the lower forms which 

 had become superfluous in the construction of the 

 more highly organised creature. However much the 

 language of evolution may force itself on biology, it 

 does no more than symbolise the results of anatomy 

 and embryology, and provide a convenient framework 

 on which these may be arranged. 



But if, as all modern experimental work shows, the 

 form of the organism is, in the long run, the result of 

 its interaction with the environment ; if, as indeed we 

 see, this form is not an immutable one, but a stage in 

 a flux ; and if deviations from it may occur with all 

 the appearance of spontaneity, then it would appear 

 that the observed facts of comparative anatomy and 

 embryology are capable of only one explanation. 

 They represent the results of an evolutionary process, 

 and the relationships that morphological studies in- 

 dicate are no longer merely logical, but really material 

 ones. We can now endeavour to utilise these results 

 in the attempt to trace the directions taken by the 

 process of evolution. 



In so doing we set up the schemes of phylogeny. 

 We divide all organisms into plants and animals, and 

 then we subdivide each of these kingdoms of life into 

 a small number of sub-kingdoms, in each of which we 

 set up classes, orders, families, genera, and species. 

 But our classification is no longer merely a formal 

 arrangement whereby we introduce order into the 

 confusion of naturally occurring things. It is now a 

 " family tree," and from it we attempt to deduce the 

 descent of any one of the members represented in it. 



The sub-kingdoms, or phyla, of organisms are the 

 primary groups in this evolutionary classification. We 



