406 ON THE ORDERS 



Reptiles afford us examples of the partial or even total 

 absence of feet ; and while we know, from the doctrine of 

 analogy, that these organs of locomotion are represented 

 in fishes by their fins, yet, in the case of such substitu- 

 tions, a new form is often adopted, in which the original 

 type is no longer recognisable. Nor ought it to surprise 

 us that these appendages of the axis should disappear, 

 still less that they should differ from their original type, 

 when we perceive that the vertebra themselves may be- 

 come obscure, as in the Chelonian reptiles, or may be 

 nearly annihilated, as in the Cyclostomous fishes. Any 

 attempt, from such considerations, to define the particular 

 living animal which is or even comes nearest to the model 

 of the Vertebrata were clearly absurd ; we can do no more 

 than endeavour to ascertain what animals possess the least 

 number of those characters which distinguish the type of 

 the group. Thus we learn to consider Reptiles and Cy- 

 clostomous fishes as the two paths by which the verte- 

 brated model is abandoned for others, and at last, finding 

 this chain interminable, are induced to confess that there 

 is no strict rule of absolute division by which a Verte- 

 brated animal may be defined. The line cannot be drawn 

 without our either leaving this division imperfect, or en- 

 croaching in some respect on the others. Still it must be 

 confessed that this uncertainty only relates to the verbal 

 definition or rule which we may choose to institute ; for 

 we are seldom in danger of mistaking a Vertebrated 

 animal either for any Cephalopoda or Annelides. The type 

 of the Vertebrata'is indeed, without being limited by words, 

 an idea much more definite, and therefore more easily 

 conceived, than that of an Annulose animal ; for if, as 

 M. Latreille has observed, we compare the organs o 



