0. C. Marsh — Origin of Mammals. 409 



Reptiles, although much lower in rank than birds, resemble 

 mammals in various ways, but this may be only an adaptive 

 likeness. Both of these classes may be made up of complex 

 groups only distantly related. Having both developed along 

 similar lines, they exhibit various points of resemblance that 

 may easily be mistaken for indications of real affinity. 



In the Amphibians, especially in the oldest forms, there are 

 hints of a true relationship with both Reptiles and Mammals. 

 It seems to me, therefore, that in some of the miDute primitive 

 forms, as old as the Devonian, if not still more ancient, we may 

 yet find the key to the great mystery of the Origin of Mammals. 



