ANATOMY OF CACOPUS SYSTOMA. 



543 



has disappeared in Rana hreviceps and Gacojnis, and the proximal 

 piece 1 has acquired a shape similar to piece 4 : this explanation 

 appeals more ingenious than natural. Further, in accordance 



Text-figure 12 (A, B, and C). 



A. The bones of a pes oi jRana liexadactyla . Lettering same as in A of text-fig. 

 11 . It will be noticed that the prehallux consists of four pieces. 



B. The same of Rana tigrina. The prehallux is made up of only two pieces, 



viz. 4 and 1; 2 and 3 have probably disappeared. One may alternatively 

 assume that 3 and 4 of R. liexadactyla have been omitted, and that 4 in 

 JK. tigrina corresponds to 2 in the latter. Lettering same as in text-fig. 11 A. 



C. The same of Sana hreviceps. The prehallux is composed of but a single piece, 

 like that of Cacopus, Lettering same as in text-fig. 11 A. 



with the function of the prehallux in these frogs, it will be a 

 distal piece which will come into direct play, and it will con- 

 sequently lend itself to an adaptation in shape and size. 



