308 



THE WONDER OF LIFE 



of the only creature by which its development can be con- 

 tinued, we should have read a great part of the riddle of 

 life. Inside the water-snail, the larva loses its cilia and 

 two eye-spots which it had ; it becomes a sporocyst which 

 falls victim to precocious asexual reproduction and forms 

 redise ; the rediae, which are larvae of a second type with 

 a food-canal and other complications, usually give rise 



FIG. 51. Three stages in the life-history of the liver-fluke (Distomum 

 hepaticum). I. The ciliated free-swimming larva, with cilia (c), 

 and eye-spots (E). II. The sporocyst stage, showing the internal 

 asexual production of another kind of larva the redia (n). III. 

 The last larval stage, the cercaria, or young fluke, showing tail (T), 

 cyst-making cells (cc), and the mouth (M). (After Thomas.) 



to more redise ; these in their turn produce again 

 asexually a third type of larva, known as the cercaria, 

 which has a bilobed food-canal, the beginnings of suckers 

 and gonads, and a locomotor tail. The cercarise leave 



