THE MICROSCOPE IN AETIOLOGY. 335 



move freely in the water. These enter a new aquatic 

 animal, snail, worm, crab, or fish, pierce into the tissues 

 and form a cyst. Thus the young, encysted, sexless disto- 

 mata arise from the Cercarise, the former received with 

 the flesh of their supporters into the stomach, and thence 

 freed from their cyst they enter other organs of another 

 animal, where they become sexually mature. 



Gen. Distomum. Two suckers on the anterior part. 

 Genital pores near the abdominal sucker. 



a. Body broad and leaf-shaped. 



11. Distomum Hepaticum. Liver-fluke. The Cercarise 

 are probably encapsuled in fresh-water snails, and eaten 

 by sheep infect them. The perfect D. hepaticum inhabits 

 numerous herbivorous mammals and occurs in man. 



b. Body more regular in form, without branched in- 

 testinal canal. 



12. D. crassum. 



13. D. Lanceolatum. Both extremities pointed. Asso- 

 ciated with D. hepaticum in the bile-ducts. 



14. D. Ophthalmobium. Once found in the crystalline 

 lens. 



15. D. heterophyes. 



c. "\Vith separate sexual apparatus. Body long and 

 slender. Female almost cylindrical. 



16. D. Hcematobium. Oral and abdominal suckers equal 

 in size. Color white. Is frequent in Egypt, in the veins 

 as well as intestinal canal and bladder. Feeds on the 

 blood. 



Gen. Monostomum. Has no abdominal sucker. 



17. Monostomum Cutis. Found once in the lens. 



2d Class. Rematelmia. Round\vorms. Bodies rounded, 

 pouched, or filamentous, without rings or segments. 

 Sometimes with papillae or hooks on anterior pole Sexes 

 distinct. 



1st Order. Acanthocephali Vertex bearing hooks. No 

 mouth or intestine. 



