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descent from branchiate forms. Siren and Pseudobranchus, 

 although especially aquatic types, exhibit the strangest anomalies 

 of development and retrogression, of use and disuse of gills. 



Many forms of Amphibia develop gills in the egg, or in the 

 intrauterine state, which are destined to serve no purpose in 

 aquatic life, even when an aquatic larval state is soon to follow. 

 Of course there may be more adaptation than we know in these 

 anomolous conditions ; but do they, in our present state of 

 knowledge, constitute a proof of adaptation or of direct response 



