230 



ZOOLOGY 



SECT. 



into the intestine, reaches the exterior with the faeces. A por- 

 tion of the egg-shell at one end then becomes separated off as 

 a sort of lid or opi'i'mlum, and gives exit to the contained embryo. 

 This, the ciliated finl/'t/o (Fig. 179, A), is a somewhat conical body 

 covered all over with vibratile cilia, and with two spots of pig- 

 ment, the eye-spots (eye], near the broader or anterior end, which is 

 provided with a triangular head-lob. ([><ip.). There is no vestige of 



B 



eye 





Fir.. 17\i.AI>. Development of Distomum hepaticum. A. ciliated 

 larva; B. sporocyst, containing redise in vaiious stages of development; 

 ' ', redia, containing a daughter redia, and eercariiw ; I>, fully developed 

 cerearia. I*. <>/>. birth opening ; o^.'eiiteron of redia ; eyi . uyi-^pots ; ijnsl. 

 gastrula stage of redia ; <A ,//(. early stages in the formation of cercari;*- : 

 't. intestine of cerearia: ,;,. m<>nila stage in the development if 

 cerearia? ; ".<. oesophagus ; <. .<c. oral sucker ; /"'/'. head-papilla of ciliated 

 i.'inliryci ; jili. pharj'nx ; jirnr. processes of redia ; ,; ,<t. su. ventral sucker. 

 (After Thomas.) 



internal organs, with the exception of a pair of name-cells. The 

 ciliated larva swims about in water, or moves over damp herbage 

 for a time, and perishes unless it happens to reach a Pond-snail 

 (Lymn(i:<i) or a Land-snail (///;//./), as a parasite of which it is 

 alone able to enter upon the next phase in its life-history. 

 When it meets with the Snail, the embryo bores into it by 

 means of the head-lobe. Established in the interior of the 



