20 



DEGENERATION : 



and represents to us more or less closely an ancestor 

 of the frog wHcli was provided with gills and tad m 

 the adult Lte, and possessed neither legs nor lungs. 



Fig. 3. —Adult shrimp of the genus Penens. 



PENEUS 

 'lernalocera ' ' "*' ' "^"^ 



Fig. 4.-Nauplms larval-form of various Crustacea (Shrimps, Water-fieas, 

 Barnacles, etc.) 



A less familiar case is that of a certain kind of 

 shrimp which is illustrated in the woodcuts (Fig. 3 

 and right lower corner of Fig. 4). The little creature 



