120 TF.MPERATURE AND FISH VERTEBRA JORDAN. 



It may be too that, as rovers in the open sea, the strong swift mem- 

 bers of the maekerel family tind a positive advantage iu the possession 

 of many vertebra', and that to some adaptation to their mode of life we 

 must attribute their lack of " ichtliyization " of the skeleton. But this 

 is wholly hypothetical, and we may leave the subject with the general 

 conclusion that with the typical Jish advance in structure has special- 

 ized the vertebrse, increased their size and the complexity of their a})- 

 pendages, while decreasing their numbe ", That with some exceptions 

 and modifications this reduction is cliaracteristic of fishes in the tropics, 

 and that it is so because in the tropics the processes of evolution aie 

 most active, so far as the fishes are concerned. 



