YOUNG BITTERLING LYING IN THE GILLS OF A FRESH-WATER MUSSEL. 

 In this strange nursery a plentiful supply of fresh water is assured, and they 

 are shielded from enemies. (After OU.) 



YOUNG PTEROPLATEA SKATE LYING IN THE OVIDUCT. 



The walls of this grow into the hinder gill-openings and pour into 



them a milky fluid, which is swallowed. 



222] 



