PROOF OF METAMOKPHOSIS IN TREMATOUES. 



31 



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

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



^iirii 





U^ 



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

 Monostomum mutabUe with the (Eediae) from the pond-snail. 



' ' necessary parasite. ' ' 



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

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



Fig. 19. — Redise. (A) with germa ; (B) with Cercariae in the interior ; (C) free Cercariae. 



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