VII. DIPLODISCUS SP. (A Trematode Worm). 



I. Crush and remove the shell from an infected snail (Gonio- 

 basis) and observe the multitudes of parasites in the liver. Place 

 the snail in a watch glass of water, and after puncturing the liver 

 with a needle observe the escape of the parasites into the water. 

 Among these the following stages may be observed: (a) Sporo- 

 cysts ; irregular hollow sac-like structures containing germ cells 

 ( eggs ) , germ balls ( many celled embryos ) , or rediae. ( b ) Rediae, 

 elongated sacks with mouth and rod-shaped intestine, beginning at a 

 pharynx in front and ending blindly behind. Xear the posterior 

 end of the body there are two processes extending out from the 

 sides of the body. ( c ) Cercariae, young trematodes with oval body 

 and a long tail. At the anterior end of the body is the anterior 

 sucker at the bottom of which is the mouth. The mouth opens 

 into the muscular pharynx, and this in turn into a bifurcated ( Y- 

 shaped) intestine. There is no anus. In the middle of the ventral 

 side is the ventral sucker. How are the suckers used ? How does 

 the cercaria swim ? Are there any cilia on the surface of the body ? 

 If possible observe the cercaria in the process of encystment. What 

 becomes of the tail? How is the cyst wall formed? (d) Encysted 

 worm: observe the little worms inside the cyst wall, (e) Mature 

 sexual forms (worms which have come out from the cyst and lived 

 for some time in the final vertebrate host ) . In mounted stained 

 specimens observe : the shape of the body as compared with that 

 of the cercaria, the posterior sucker (acetabulum), and the sexual 

 organs, the testes two in number, one on either side of the body 

 about half way from the anterior to the posterior ends, the single 

 ovary in the median line some distance posterior to the testes, the 

 small lobulated shell gland near the ovary, and the large vitellaria, 

 one on either side, lying partly above and partly below the intestine. 

 The main trunks of the water vascular system will be seen along 

 the sides of the body lying in folds beside the intestine. The excre- 

 tory bladder is situated at the posterior ends of the body. It re- 

 ceives the posterior ends of the two lateral excretory trunks and 

 opens to the exterior on the dorsal side of the body. 



Make drawings of all the stages observed. 



VIII. CROSSOBOTHRIUM OR TAENIA SP. 



(A Tapeworm). 



i. Examine an adult worm and notice that the bodv is flat and 



mf 



jointed. 



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