THE PROGRESS OF DEGRADATION. 165 



Tlie progress of the ichthyic tail, as recorded in geologic 

 history, corresponds with that of the ichthyic limbs. And 

 as in the existing state of things we find fishes that nearly 

 represent, in this respect, all the great geologic periods, — I 

 say nearly^ not fully, for I am acquainted with no fish ade- 

 quately representative of the period of the Old Red Sand- 

 stone, — it may be well to cast a glance over the contemporary 

 series, as illustrative of the consecutive one. In those placoids 

 of the shark family that to a large brain unite homological 

 symmetry of organization, and represent the placoids of the 

 first period, we find, as I have already shown, that the vei'- 

 tebrse gradually diminish in the caudal division of the co- 

 lumn, until they terminate in a point, — a circumstance in 

 which they resemble not merely the betailed reptiles, but also 

 all the higher mammiferous quadrupeds, and even man him- 

 self. And it is this peculiarity, stamped upon the less de- 

 structible portions of the framework of the tail, — vertebrae 

 and processes, — rather than the one-sided or heterocercal 

 form of the surrounding fin, composed of but a mucoidal 

 substance, that constitutes its grand characteristic ; seeing 



spheres is the proper business of life, than the non-degraded orders and 

 famihes. The objection is, however, a possible one, and one which a 

 single remark may serve to obviate. It is certainly true that the de- 

 graded families are thoroughly fitted for the performance of all the work 

 given them to do. They greatly increase when placed in favourable cir- 

 cumstances, and, when vigorous and thriving, enjoy existence. But then the 

 game may be said of all animals, without reference to their place in the 

 scale : the mollusc is as thoroughly adapted to its circumstances, and as 

 fitted to accomplish the end proper to its being, as the mammiferous 

 quadruped, and the mammiferous (quadruped as man himself ; but the 

 fact of perfect adaptation in no degree invalidates the other not less cer- 

 tain fact of difference of rank, nor proves that the mollusc is equal to the 

 quadruped, or the quadruped to man. And, of course, the remark 

 equally bears on the reduced as on the unelevated, — on lowness of place 

 when a result of degradation in races pertaining to a higher division of 

 animals, as on lowness of place when a result of the humble standing of 

 the division to which the races belong. 



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