I50 THE COMMON FROG. [chap. 



blances ; first, as regards the orders of its class, and 

 secondly, as regards the class itself. 



1. Its own order, Anoiira, has been seen to present 

 singular resemblances to the Chelonia amongst 

 reptiles. Such are the bony plates of the back in 

 some forms, the bony covering of the temporal fossa 

 in others, the mode of inspiration in the adult, the 

 armature of the jaws in the young. In contrast with 

 this the peculiar elongated tarsus has reminded us of 

 certain mammals, and the median Eustachian opening 

 of Pipa and Dactyleihra has suggested an affinity to 

 crocodiles and birds. It has been plain, however, that 

 these several likenesses, however singular and striking, 

 are not evidences of genetic affinity. 



2. The order Urodcla may well recall to mind the 

 Lacertilia amongst reptiles, with which animals the 

 Urodela were actually classed by Linneus. Moreover 

 in both groups we find a series of different species, 

 longer and longer in body and shorter and shorter in 

 limb. We have also seen that in both these groups 

 an analogous complication obtains in the muscles of 

 the legs. 



3. The order OphiomorpJia, as has been before ob- 

 served, present a general resemblance to serpents, and 

 a special resemblance 'to certain short-tailed ones ; 

 though it is rather with the Amphisbenian Saurians 

 that they may most advantageously be compared. 

 Here again, however, we m^eet with the resemblances 

 which, though striking, do not allow themselves to be 

 interpreted as indices of any special relationship by 

 descent. 



4. The order LabyrintJwdonta recalls to mind, as 



