42 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



At first the only skeleton of these lateral rods 

 consisted of parallel rods of a tough material. By 

 the transformation of these rods, the skeleton of 

 the limbs of vertebrates was ultimately formed. 



The skeleton of limbs then consisted originally 

 of a certain number of parallel rods. One of these 

 rods, lying in the long axis of the future limb, 

 became longer than the others, while the neigh- 

 bouring rods began to slant, so that those nearest 

 to the elongated rod spread out like a fan, and 

 gradually moved outwards along the principal rod. 

 This phenomenon was repeated several times, so 

 that eventually those rods nearest to the principal 

 rod passed towards the free end of it, and as the 

 others followed in the same direction, the fin finally 

 acquired a feather-like structure. 



This transformation of the continuous folds into 

 limbs a progressive transformation, since new and 

 more perfectly adapted organs were formed was 

 accompanied by degeneration, for a considerable 

 part of the folds disappeared. In the same way, 

 although the transformation of the parallel rods 

 into bipinnated fins constituted a development, 



C. Palceontological proofs : 



(a) The series of paired spines in Diplacanthus and in 



Climatius between the pectoral and ventral spines. 



(b) The skeleton of the fins of Cladoselaclie. 



D. Philogenetic proof: The necessity of the bifurcation of the 



unpaired folds at the anal region (Sternarchus). 



E. Physiological proof: The lateral folds are the undifferenti- 



ated condition of organs of equilibrium in modern fish. 



