Ill 



PLATODES LIFE-HISTORY OF TREMATODA 



169 



egg shell and swims about freely (B). It is club-shaped ; at the thicker 

 anterior end it has a small median prominence, behind this an X-shaped 

 eye spot, and under this a ganglion, and further a granulated mass which 

 is considered to be the intestinal rudiment. We can also recognise 2 

 ciliated cells of the excretory system. The greater mass of the body, 

 however, is formed of germ cells, which are considered to be partheno- 



FIG. 119. Life-history of Distoma hepaticum, after Leuckart. A, Egg with embryo. B, 

 Free- swimming ciliated embryo ; o, eye spot. C, Sporocyst. D, E, and F, Redias ; ph, pharynx ; 

 go, birth aperture ; d, intestine. G, Cercaria ; ms, oral sucker ; n, nerve ganglia ; fcs, ventral 

 sucker ; gd, forked branches of the intestine ; cd, glands, whose secretion yields the cysts. 

 H, Encysted young Distoma ; c, cyst. I, Young Distoma in the sheep's intestine. 



genetic eggs, possessing the capacity, of developing without being 

 fertilised. These germ cells divide (furrow) early, and become cell 

 spheres. 



The embryos must meet with a water-snail, Limnceus truncatulus, and 

 penetrate into its respiratory cavity in order to develop further. They 

 here lose the covering of cilia ; the eyes, the ganglion, and the granulated 

 mass become disorganised. Their bodies represent a pouch, containing 



