CHAPTER VIII 



habitudes and attitudes 

 (bionomical convergence) 



Identity of habitat occasions convergence of 

 habits on the part of diverse animals. A great 

 deal of this has been implied in the preceding 

 chapters, but more remains to be said. The three 

 principal functions of animal life, at least above 

 the level of the sponge, are metabolism, 1 repro- 

 duction, and neuration, the last being at once the 

 master and the servant of the others, and leading 

 on from a lower to a more advanced cerebration. 

 The number of phyla or leading types of the 

 animal kingdom is considerable, and there are 

 only these three primary functions upon which 

 to ring the changes. 



If there is one aspect of convergence more 

 widespread than another, it is that of cerebral 

 convergence, which is associated with the pheno- 

 menon of cephalisation or head-formation ; and 

 we can infer from this circumstance how hope- 

 less must be the search for neural homology as 



1 Metabolism comprises nutrition, respiration, and excretion. 



113 H 



