160 ESSAY ON CLASSIFICATION. 



from the earliest times, during which only the lowest 

 types of animals were represented, to the last period, 

 when Man appeared at the head of the animal crea- 

 ttion. 1 It has already been shown, (Sect. VII.), that 

 representatives of all the great types of the animal king- 

 dom have existed from the beginning of the creation of 

 organized beings. It is not, therefore, in the successive 

 appearance of the great branches of the animal kingdom, 

 that we may expect to trace a parallelism between their 

 succession in geological times and their relative standing 

 at present. Nor can any such correspondence be observed 

 between the appearance of classes, at least not among 

 Eadiata, Mollusks, and Articulata, as their respective 

 classes seem to have been introduced simultaneously 

 upon our earth, with perhaps the sole exception of the 

 Insects, which are not known to have existed before the 

 Carboniferous period. Among Vertebrata, however, there 

 already appears a certain coincidence, even within the 

 limits of the classes, between the time of their intro- 

 duction, and the rank which their representatives hold in 

 comparison with one another. But upon this point more 

 hereafter. 



It is only within the limits of the different orders of 

 each class, that the parallelism between the succession of 

 their representatives in past ages and their respective 

 rank in the present period, is decidedly characteristic. 

 But if this is true, it must be at the same time obvious to 

 what extent the recognition of this correspondence may 

 be influenced by the state of our knowledge of the true 

 affinities and natural gradation of living animals, and 

 that, until our classifications have become the correct ex- 

 pression of these natural relations, even the most striking 



1 AGASSIZ, (L.,) Twelve Lect., etc., p. 68 and p. 128. 



