THE ORIGIN OF VERTEBRATE LIMBS 427 



form the "musculi radiales" takes place before the appearance 

 of the rays. 



The writer's investigations on Cestracion show conclusively 

 that such an argument cannot be considered valid, for the reason 

 that fusion occurs also in all the unpaired fins, which are held by 

 the gill-arch theorists to be strictly metameric. I have carefully 

 traced the process from its inception and compared it with the 

 same process in the paired fins and there is no observable dif- 

 ference. On the other hand, it only shows more clearly the 

 close relation of the paired and unpaired fins. 



VI. The discordance or discrepancy between muscles and 

 rays which has also been strongly urged as proof of the primitive 

 dysmetamery and independent origin of these structures in the 

 paired fins (Braus '04) has likewise no place in argument against 

 the fin-fold theory, for again the same condition is found to 

 occur in the unpaired fins. My reconstructions of the first and 

 second dorsal fins of Cestracion show the same sort of discrepancy 

 that has been proved to exist in the paired fins. 



In the foregoing pages the objections to the fin-fold theory 

 have been considered; we may now mention the following 

 objections to the gill-arch theory: 



I. The indications are that the primitive fin possessed a 

 far greater number of rays than the primitive gill. 



II. There has never been discovered any indication of an 

 intermediate stage representing a transition from the gill to the 

 fin. 



III. My observations indicate that the paired fin girdles 

 have not been abstracted from the branchial region by the 

 spinal muscles in the manner assumed by the gill-arch theorists. 



IV. The gill-arch theory violates important time and place 

 relations. 



To further explain these statements : 



I. The gill-arch theorists have tried to show that the gill 

 rays have degenerated, and they reason that at one time the 

 gill might have had rays enough to equal those of the primitive 

 fin. The only evidence of degeneration thus far produced has 

 been in the hyoid arch, the rays of which are reduced somewhat 



