FOSSIL PEDIGREES 77 



and the result has been a wholesale revision of former notions 

 concerning phylogeny. ''I could easily," says Bather, "occupy 

 the rest of this hour by discussing the profound changes 

 wrought by this conception on our classification. It is not 

 that orders and classes hitherto unknown have been discov- 

 ered, not that some erroneous allocations have been corrected, 

 but the whole basis of our system is being shifted. So long 

 as we were dealing with a horizontal section across the tree of 

 life — that is to say, with an assemblage of approximately 

 contemporaneous forms — or even with a number of such hori- 

 zontal sections, so long were we confined to simple description. 

 Any attempt to frame a causal connection was bound to be 

 speculative." {Ibidem, p. 258.) Whether zoologists will take 

 kindly to this ''shifting of the whole basis" of classification, 

 remains to be seen. Personally, we think they would be very 

 ill-advised to exchange the solid observational basis of homol- 

 ogy for the scanty facts and fanciful interpretations of 

 palaeontologists. 



The second stumblingblock in the path of Transformism 

 is the occurrence of convergence. We have seen that, in the 

 palseontological argument, descent is inferred conjointly from 

 similarity and succession, and that, in the abstract, this argu- 

 ment is very persuasive. One of the concrete phenomena, 

 however, that tend to make it inconsequential, is the undoubted 

 occurrence of convergence. Prof. H. Woods of Cambridge, in 

 the Introduction to the 5th edition of his "Palaeontology" 

 (1919), speaks of three kinds of convergence (cf., pp. 14, 15, 

 16), which, as a matter of convenience, we may term the 

 parallelistic, the radical, and the adaptational, types of con- 

 vergence. A brief description of each type will serve to elu- 

 cidate its nature and its significance : 



(1) Parallelistic convergence implies the appearance of 

 parallel modifications in the homologous parts of organisms 

 regarded as diverging from common stock in two distinct col- 

 lateral lines, that were independent at the time of the ap- 

 pearance in both of the said parallel modifications. Speaking 



