A PECULIAR MONSTROSITY IN A FROG. 



315 



so far as I know. One might expect that by operating on one 

 of the Anlagen a supernumerary arm, such as that of Button's 

 case, could be produced. It is an experiment that some skilful 

 operator should attempt to perform. But the Anlagen of the 

 two limbs are here not closely approximated ; they are far apart. 

 A simultaneous operation on both is not possible, and an accident 

 in nature equally affecting both is in the highest degree improb- 

 able. 



It appears much more probable to me that in the frog here 

 described we have a case quite parallel to that in Fig. 3, which is 



FIG. 2. 



properly designated, according to Schwalbe ('07), as a Thor- 

 acopagns parasiticus . The generally accepted, and to me very 

 probable, explanation of these forms is that they started with a 



