CHAPTER III 

 THE LIFE CYCLE OF A TYPICAL TREMATODE 



TECHNICAL SUGGESTIONS 



For the study of the characteristic operculate eggs, the most certain 

 source of supply is in the various species of frog trematodes. Per- 

 manent mounts, in balsam, are convenient. 



Living miracidia are readily obtained from the eggs of Diplodiscus 

 from the rectum, or of various Gorgoderince from the bladder of frogs. 

 Placed in water at room temperature they will hatch overnight. If 

 wanted more promptly, the miracidia will emerge within a half hour 

 or so if placed in water heated to 35 to 40°C. For permanent mounts 

 they may be collected in a watch glass with a minimum of water, killed 

 in hot saturated corrosive sublimate solution, stained in borax car- 

 mine, and mounted in balsam in the usual manner. 



For the study of the larval stages, snails should be collected from 

 different localities, as considerable variation in intensity of infection 

 as well as in species occurs. The best sources of material may be 

 determined in advance of laboratory work by sorting as to species the 

 snails from different localities and placing a half dozen specimens of 

 each group in wide-mouthed 8-ounce bottles one-third full of water. 

 Kept in this manner overnight the cercariae escape and the intensity 

 of infestation of the various groups can be determined by examining 

 the water. Infected snails may be kept alive and will continue to 

 discharge cercariae for months if the water is changed frequently and 

 lettuce is provided for food. 



Permanent balsam mounts may be made after fixing in hot corrosive 

 sublimate or in one of the picro-formal fixatives. 



THE LIFE HISTORY OF THE SHEEP LIVER FLUKE 



Preparatory to the practical work the student should review 

 the life cycle of the sheep liver fluke, a form very generally 

 discussed in beginning courses in zoology. 



The adult fluke in the bile ducts of the liver deposits eggs 

 which pass into the intestine of the host and out with the drop- 

 pings. These eggs are operculate and develop the ciliated 

 embryo, or miracidium. After two or three weeks in water the 

 miracidium escapes and bores into the pulmonary chamber of a 

 particular species of snail where it transforms into a sporocyst, an 

 irregular mass without cilia and without a digestive tube. 



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