PHENOMENA OF REGRESSION AND CONVERGENCE 219 



most remarkable proofs of the transformist hypo- 

 thesis. 



Cope has endeavoured to show, with the support 

 of many documents, that the palseontological evo- 

 lution of the Vertebrates was at one time progressive 

 and at another regressive. This means that the 

 necessity for adaptation to needs has led sometimes 

 to the augmentation of the constituent parts of an 

 apparatus, at others to a diminution in the number 

 of those parts. Thus, the hand of the Bird, with 

 its three metacarpal bones and its three fingers with 

 the elements stuck together or atrophied, is a 

 reduction relatively to the normal pentadactyl hand 

 of a Reptile or a Primate. On the other hand, the 

 natatory paddle, with its multiple elements, of an 

 ichthyosaurus, intimates a progressive adaptation. 

 Naturally, the reduction only affects certain organs 

 or certain apparatus ; thus the Mammals are in 

 a state of regression compared with the Reptiles, 

 by reason of the atrophy of the pineal gland and 

 of the coracoi'd bone. There is only, according to 

 Cope, a complete regression (degeneration) when 

 the sum of the subtractions is greater than the 

 sum of the additions.* 



The phenomena of regression have thus acted 

 in the evolution of fossil animals a rather notable 

 part, which modern palaeontologists have striven to 

 set forth with sometimes, perhaps, a little exaggera- 

 tion. For, as among living animals, the regressive 

 characteristics of fossil beings may relate either to 



* The analysis given above of the work of Cope is referred to for 

 further details on these ingenious and philosophical ideas of the 

 learned American naturalist. 



