CHAPTER VI 



DIVERGENCE AND PARALLELISM 



FEW things are more astonishing at first acquaint- 

 ance than examples of close convergence, whether 

 mimetic or homoplastic, because they appear para- 

 doxical and contrary to expectation. In fact the 

 ways of convergence are devious, many-hued, 

 illuminating, full of surprises, inviting away from 

 the narrow path of homology which, at least in 

 extreme cases, begins and ends in obscurity. It 

 must, however, be acknowledged that the pioneer 

 work which effected the discovery of the pelagic 

 larvae of so many marine animals about the 

 middle of the nineteenth century, was thoroughly 

 satisfactory, and seemed to indicate to a later 

 generation that the pursuit of homology as an 

 aid to phylogeny was not wholly elusive. If 

 there has been any mistake it has been that of 

 not defining the different degrees of homology. 

 But there is no necessity to dwell upon mistakes 

 nor to regret them. 



As a seeming paradox there comes the pre- 

 liminary axiom that convergence depends firstly 

 on divergence and secondly on parallelism. As 



69 E 2 



