282 EXPLANATION OF THE PLATES. 



Cercarice : a oesophogeal csecum, or rudiment of an alimentary 

 canal. This is really the second of the redial forms figured by 

 Steenstrup. 



Fig 10. Cercaria, or larva form of the Distoma, being one of 

 the brood figured in the last. 



Fig. 11. Ultimate form of Distoma, produced by a transfor- 

 mation of the last during its stage of encystment. 



Fig. 12. Myrianida fasciata from M. Edwards showing the 

 formation of caudal zooids, as described at page 101. 



