G8 ESSAY ON CLASSIFICATION. 



and New Holland. There are none with three and four 

 toes, either in the fore feet or in the hind feet. Those 

 with four toes to the fore feet live in New Holland ; those 

 with five toes to the fore feet and four to the hind feet, 

 in Bengal ; and with four toes to the fore feet and five to 

 the hind feet, in Africa, the West Indies, the Brazils, and 

 New Holland. Those with five toes to all four feet have 

 the widest distribution ; and yet they are so scattered that 

 no single zoological province presents any thing like a com- 

 plete series. On the contrary, the mixture of some of the 

 representatives with perfect feet with others which have 

 them rudimentary in almost every fauna, excludes still 

 more decidedly the idea of any influence of physical agents 

 upon this development. 



Another similar series, not less striking, may be traced 

 among the tailed Batrachians ; for the characters of which 

 I may refer to the works of Holbrook, Tsclmdi, and 

 Baird, 1 even though they have not presented these animals 

 in this connection ; as the characteristics of the genera will 

 of themselves suggest their order, and further details upon 

 this subject would be superfluous for my purpose, the 

 more so as I have already discussed the gradation of these 

 animals elsewhere. 2 



Similar series, though less conspicuous and more limited, 

 may be traced in every class of the animal kingdom, not 

 only among living types, but also among the represen- 

 tatives of past geological ages ; which adds to the interest 

 of such series, as showing that such combinations in- 

 clude not only the element of space, indicating omni- 



1 HOLBROOK (J. E.), North Ameri- trachia ; Journal Acad. Nat. Science, 



can II erpetology; Philadelphia, 1842, of Philadelphia, 2nd series, vol. i, 



4to., 5th vol. TSCHUDI (J. J.), Clas- 1849, 4to. 



sification cler Batrachier; Neuchatel,- 2 AGASSIZ (L.), Twelve Lectures 



1838, 4to. BAIRD (Sp. F.), Revision on Comparative Embryology; Boston, 



of the North American Tailed Ba- 1849, 8vo., p. 8. 



