The Skeleton of the Fish 61 



showing traces of a triple division. Along the middle of the 

 fin runs a jointed axis gradually becoming smaller and thinner 

 towards the extremity. Each joint bears on each side a three-, 

 two-, or one-jointed branch." 



In the genus Lepidosiren, also a Dipnoan, the pectoral limb 

 has the same axial structure, but is without fin-rays, although 

 in the breeding season the posterior limb or ventral fin in the 

 male is covered with a brush of fine filaments. This structure, 

 according to Prof. J. G. Kerr,* is probably without definite 

 function, but belongs to the "category of modifications so often 

 associated with the breeding season (cf. the newts' crest) com- 

 monly called ornamental, but which are perhaps more plausibly 

 looked upon as expressions of the intense vital activity of the 

 organisms correlated with its period of reproductive activity." 

 Professor Kerr, however, thinks it not unlikely that this brush of 

 filaments with its rich blood-supply may serve in the function 

 of respiration, a suggestion first made by Professor Lankester. 



* Philos. Trans., Lond., 1900. 



