STRUCTURE AND DEVELOPMENT OF LEI'IDOSTEUS. 799 



logous with those of the tail, but are formed by a connecting 

 piece between the basal stumps (haemal processes), which origi- 

 nates as a paired median process of these stumps." 



The incomplete homology between the anterior haemal arches 

 and the true caudal haemal arches which follow them is exactly 

 what we suggest may be the case in Elasmobranchii, and if it be 

 admitted in the one case, we see no reason why it should not 

 also be admitted in the other. 



If this admission is made, the only ground for not regarding 

 the ribs of Elasmobranchii as homologous with those of Ganoids 



FIG. 3 . 



Semi-diagrammatic transverse sections through the first caudal vertebra (A), the last 

 trunk vertebra (B), and the two trunk vertebra.- in front (C and D), of a Salmon 

 embryo of 2-3 centims. (From Gotte.) 



nb., hcemal arch; nb'., hcemal process; lib"., rib; c., notochord ; a., aorta; v., vein; 

 h., connecting pieces between hcemal processes ; it., kidney ; d., intestine ; 

 sp'., hremal spine ; in'., muscles. 



is their different position, and we have already attempted to 

 prove that this is not a fundamental point. 



The results of our researches appear to us, then, to leave two 

 alternatives as to the ribs of Fishes. One of these, which may 

 be called Gotte's view, may be thus stated: The haemal arches 



