THE DEVELOPMENT OF ORGANISMS 



771 



This leads us to what is familiar in ferns and their allies — the 

 alternation between an inconspicuous male-and-female prothallus, 



REDIAE 



5P0R0CYST 



Fig. i2i 



The Four Chapters in the Life-History of a Liver-Fluke. (i) The adult, 

 natural size, with its pharynx (ph), adhesive sucker (s), and much- 

 branched gut {g). (2) The much magnified free-swimming ciliated larva 

 or miracidium, with its two eye-spots (e). (3) The sporocyst and redia 

 stages. R, redia developing inside a sporocyst or another redia. A simple 

 food-canal {g) in a redia. C, young cercariae inside final generation of 

 rediae. (4) Much magnified free cercaria, showing (g) the beginning of 

 the gut, (5) the adhesive sucker, and {t) the locomotor tail. 



a little green disc found in wet, shady places, and the conspicuous 

 vegetative spore-producing fern-plant with its beautiful fronds. 



