Reproduction and Development 47 



excreta. Here, in damp places, pools, and ditches, free 

 and active embryos are hatched out of the eggs. Each 

 embryo (Fig. 10, C, much enlarged) is covered with ciha, 

 except at the anterior end, which is provided with a head- 



Fig. 10. — Liver-fluke : Embryonic stages. (After A. P. Thomas.) 



A. Ovum : em., embryo ; op., operculum. B. LimncEus truncatulus (natural size). C. Free 

 embryo: e.s., eye-spot; ex., excretory vessel; g.c, germinal cells; h.p., head-papilla. D. 

 Embryo preparing to become a sporocyst : g.c, germinal cells. E. Sporocyst : g., gastrula ; 

 VI., morula; re., redia. F. Redia: b.o., birth-opening; ce., cercaria; col., collar; di., digestive 

 sac; ph., pharynx; p.pr., posterior processes; re., daughter redia. G. Cercaria: cyi., cysto- 

 genous organ ; di., digestive sac ; o.s., oral sucker ; p.s., poeierior sucker ; ph., pharynx. 



papilla (h.p.), "When the embryo comes in contact with 

 any object, it, as a rule, pauses for a moment, and then 



