Note on the Pectoral Fin of the Sole, Achirus capensis. 
Ill 
(a) Cymnopleura, with simple respiratory mechanism and no opercula 
nor limbs, including Hemichorda, Cephalochorda, Urochorda and Cyclo- 
stomata, each of which might also be rearranged on the same basis. 
(b) Cladopleura, with complex respiratory mechanism and paired limbs, 
including fishes with paired limbs derived from opercula (Tetraptera), and 
Amphibia, etc., with paired limbs derived from opercula modified as external 
gills (Tetrapoda). 
