The Rot in Sheep. 



55 



from ova, but from gemma?, which differ essentially from ova. 

 They are solid, round, and somewhat flattened discs, which, 

 growing and developing, become little caudate worms, resem- 

 bling in form and organisation certain Trematoda (Distoma, 

 Monastoma, &c). 



Fig. 11 represents on a large scale the progressive develop- 

 ment of a cercaria as it goes on within the sac from the first bud 

 or sporule to the perfect embryo. A reference to the figures will 

 show — 1, a sporule ; 2, sporule elongating ; 3, sporule becoming 

 caudated ; 4, early form of cercaria ; and 5, perfect embryo. In 

 the last-named figure, a indicates the oral aperture ; c, d, the 

 urinary organ ; <?, the tail ; and f, two pigment-spots. 



When first set free from the sac the cercaria is rather tardy in 

 its action, but after a time it swims freely about, assisted in its 

 various movements by the length of its tail. Fig. 12, which we 



Fig. 12. 



A fully developed Cercaria ephemera. After Huxley. 



here insert, shows a fully developed Cercaria ephemera^ the body 

 of which, it will be noticed, bears a strong resemblance to ;i 

 fluke. In this figure, a represents the mouth : 6, the alimentary 

 canal ; c, d, the urinary organ ; e, the tail ; and /* pigment- 

 spots. It is worthy of note thai in the most perfected cercaria 



