[Annals N. Y. Acad. Sci., Vol. XVII, No. 2, Part II, pp. 415-436. 



THE ORIGIN OF VERTEBRATE LIMBS. 



RECENT EVIDENCE UPON THIS PROBLEM FROM STUDIES ON PRIM- 

 " ITIVE SHARKS. 



By Raymond C. Oseur 



N. 



For nearly thirty years the Fin-fold Theory has been commonly 

 accepted to explain the origin of the limbs of the Vertebrata. 

 This theory has as its main thesis that all fins, both paired and 

 unpaired, have arisen in situ and in the same manner, as local 

 developments from the body wall. Thus conceived, they are 

 primarily external structures which have as their primitive form 

 a longitudinal fold of skin supplied with muscles, nerves, and 

 blood-vessels derived in a segmental way from the adjoining 

 body wall, and with supporting structures which have had their 

 origin within the fins. This theory first took form in the work 

 of Thacher ('77), Mivart ('79), and Balfour ('78), all of whom 

 arrived at the same conclusion independently, the first two on 

 anatomical grounds, the last from the embryological standpoint. 

 The theory has been ably supported by Dohrn ('83 and '02), 

 Paul Mayer ('86), Wiedersheim ('92), Mollier ('93), Rabl (01)' 

 Dean ('02), Regan ('04), and others. 



Opposed to this view is the older " Archipterygium " or Gill- 

 arch Theory, first definitely stated by Gegenbaur ('65 and '70) 

 and maintained by him through all his later work ('95). Ranged 

 on this side of the question are Bunge ('74), von Davidoff ('79 

 and '80), Furbringer ('96 and '02), Braus ('98 and '04), and others 

 of the Gegenbaur school. As far as the origin of the unpaired 

 fins is concerned, the gill-arch theorists admit that they arose 

 as local outgrowths, and go farther than their opponents in 

 assuming a rigid metamerism of all the structures of the unpaired 



415 



