3o8 



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 redise, which are larvse of a second type with 

 a food-canal and other comphcations, 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 (b). III. 

 The last larval stage, the ceroaria, 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 



