28 ESSAY ON CLASSIFICATION. 



animal kingdom points to the necessity of a radical 

 reform in the nomenclature of Comparative Anatomy. 1 

 Some naturalists, however, have already extended such 

 comparisons respecting the structure of animals beyond 

 the limits within which they lead to correct results, when 

 they have attempted to show that all structures may be 

 reduced to one norm, and when they have maintained, 

 for instance, that every bone existing in any Vertebrate 

 must have its counterpart in every other species of that 

 type. To assume such a uniformity among animals would 

 amount to denying to the Creator even as much freedom 

 in expressing his thoughts as man enjoys. 



If it be true, as pointed out above, that all animals are 

 constructed upon four different plans of structure, in such 

 a manner that all the different kinds of animals are only 

 different expressions of these fundamental formulae, we 

 may well compare the whole animal kingdom to a work 

 illustrating four great ideas, between which there is no 

 other connecting link than the unity exhibited in the 

 eggs in which their most diversified manifestations are 

 first embodied in an embryonic form, to undergo a series 

 of transformations, and appear in the end in that won- 

 derful variety of independent living beings which inhabit 

 our globe, or have inhabited it from the earliest period of 

 the existence of life upon its surface. 



The most surprising feature of the animal kingdom 

 seems to me, however, to rest neither in its diversity, nor 

 in the various degrees of complication of its structure, nor 

 in the close affinity of some of its representatives while 

 others are so different, nor in the manifold relations of all 



1 See AGASSIZ (L.), On the Struc- Proc. of the Amer. Assoc. for the 



ture and Homologies of Radiated Ani- Adv. of Science for 1849; Boston, 



rnals, with Reference to the System- 1850, 1 vol. 8vo., p. 389. 

 atic Position of the Hydroid Polypi, 



