PROOF OF METAMORPHOSIS IN TREMATODES. 



31 



ment of germ-granules in their interior, to a brood of animals which 

 resemble the tailed Treniatodes, but, unlike them, swim about freely 



FIG. 17. Infusorian-like embryos of FIG. 18. Bojanus' "kingsyellow worms" 

 Monostomum mutabile with the (Redise) from the pond-snail, 



"necessary parasite." 



in water (Fig. 20), and had for this reason been included by the older 

 naturalists among the Infusoria (under the name of Cercaria). 



c. 



FIG. 19. Redise. (A) with germs ; (B) with Cercariae in the interior ; (C) free Cercariae. 



