OPALINID CILIATE INFUSORIANS — METCALF 



593 



cold, glacial streams. Their tadpoles carry ProtoopaHnas of subgenus 

 II brought from Asia, but in the cold water of these streams their 

 metamorphosis is delayed until the second year, so that opalinid 



Figure 148.— Geographic distribution of the Pipidae. 



Figure 149.— Geographic distribution of the DiscoglossiUae 



infection is from the tadpoles of the former year to the young tadpoles 

 of the later year. As is so often the case when tadpoles Uve mto the 

 second season, the adult anurans are not infected (cf . Rana catesheiana, 

 R. clamitans). The evolution of Ascaphus into its decadent character 



166877 — 40 9 



