20 



DEGENERATION : 



and represents to us more or less closely an ancestor 

 of the frog which was provided with gills and tail in 

 the adult state, and possessed neither legs nor lungs. 



FIG. 3. Adult shrimp of the genus Peneus. 



LERNAEOCERA 



FIG. 4. Nauplius larval-form of various Crustacea (Shrimps, Water-fleas, 

 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 



