128 



EXPLANATION OF 



PLATE III. 



Figs. 1-6. The Development of the Distoma tarda. 



N.B. AU the figures are from original drawings, 

 and under the same magnifying power, except 

 figs. 1 y, 4i a, and 6 b, which are but httle mag- 

 nified. 



Fig. 1. The development of a series of sacciform crea- 

 tures which occur on the viscera of the snail, and 

 appear to be the "nurses" of young, which after- 

 wards assume the Distoma-iorm : Distoma-" 'HVrs^s." 

 From extremely minute, oval or pyriform bodies, 

 1 a, and 1 d, they are formed into longer or shorter, 

 more or less regular bodies possessing a vermicular 

 motion, 1 c. Id, 1 d', and inclosing a cavity in 

 which a multitude of germs are placed which are 

 commencing their development. 1 e, an individual 

 possessing rather more powerful vermicular motion, 

 and presenting half- developed embryos ; the resem- 

 blance which these embryos bear to the Distoma- 

 larvce is akeady apparent. 1/, an individual which 

 has lost all its power of motion, and whose skin has 

 become distended almost into a delicate membrane 

 by the vast crowd of embryos (viz. developed Cer- 

 carice). \g, an assemblage of these Distoma nurses 

 as they usually appear when covering the internal 

 organs of the snail. 



