224 



Dr. A. Giiuther on Ceratodus, 



sistent, tlie lateral brandies being either entirely absent (as in 

 the former), or quite rudimentary (as in the latter). In all these 

 cases the analogy of this structure to the diphyoccrcy of the 

 terminal portion of the tail is apparent, whilst a hetcrocercal 

 condition is rei)resentcd in the pectoral fin of Acipenser. In 

 this fish the axis {h) is not inserted in the longitudinal median 



Ceratodus. Acipcnser. 



rt, cai'pal cartilage ; fc, jointed axis ; c, branches having- the carpus as base ; 

 (7, branches liaving tlie axis as base. 



line of the carpus (a), but quite at the inner corner; conse- 

 quently brandies exist on one side of the axis only, viz. on 

 that side on which they are needed for the support of the fin- 

 rays. The axis is comparatively sliort and feeble, composed 

 of three joints, and forming the base for three branches [d). 

 Three other branches (c) are inserted immediately into the 



