52 ESSAY ON CLASSIFICATION 



bution of these so closely linked genera, inscribed after their names, 

 we perceive at once that they are scattered all over the globe, but not 

 so that there could be any connection between the combinations of 

 their structural characters and their homes. The types without legs 

 are found in Europe, in Western Asia, in Northern Africa, and at 

 the Cape of Good Hope; the types with hind legs only, and with one 

 single toe, at the Cape of Good Hope, in South America, New Hol- 

 land, and New Guinea; those with two toes at the Cape of Good 

 Hope only. Among the types with four legs the origin of those with 

 but one toe to each foot is unknown, those with one toe in the fore 

 foot and two in the hind foot are from South Africa, those with two 

 toes in the fore foot and one in the hind foot occur in the Philippine 

 Islands, those with two toes to all four feet in New Holland, those 

 with three toes to the hind feet and two to the fore feet in Algiers 

 and Ne^v Holland; none are known with three toes to the fore feet 

 and two to the hind feet. Those with three toes to the fore feet in- 

 habit Europe, Northern Africa, 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 in the fore feet and five in 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 scat- 

 tered that no single zoological province presents any thing like a 

 complete series. On the contrary, the mixture of some of the repre- 

 sentatives with perfect feet with others which have them rudimen- 

 tary, in almost every fauna, excludes still more decidely the idea of 

 an influence of physical agents upon this development. 



Another similar series, not less striking, may be traced among the 

 Batrachians, for the characters of which I may refer to the works of 

 Holbrook, Tschudi, and Baird,'^" even though they have not pre- 

 sented them 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.'^^ 



■'"John E. Holbrook, North American Herpetology (5 vols., Philadelphia, 1842-1843); 

 Johann J. von Tschudi, Classification der Batrachier (Neuchfitel, 1838); Spencer F. 

 Baird, "Revision of the North American Tailed Batrachia," Journal, Academy of 

 Natural Sciences of Philadelphia, I (2d ser., 1849), 281-294. 



" Agassiz, Twelve Lectures on Embryology, p. 8. 



