PNEUMONECES, CRYPTOCOTYLE 73 



CRYPTOCOTYLE 



One of the most favorable digenetic trematodes for study 

 of the life history is Cryptocotyle lingua. Adults of this 

 species are found in the intestine of fish-eating birds and 

 mammals. Larval stages may be found in the common 

 marine snail, Littorina litorea. 



Observe the living and preserved adult Cryptocotyle and 

 make a drawing to show the difference in morphology be- 

 tween this species and Pneumoneces. 



The Rediae. — Remove Littorina litorea from its shell. If 

 the liver is grayish, shrunken and irregular in appearance it 

 will be found to contain numerous rediae and cercariae. 

 Transfer to a slide and study. Note the following: 



(a) Rediae with characteristic mouth and pharynx. 



(b) The numerous cercariae in various stages of develop- 

 ment. 



The Cercaria. — Obtain, from the assistant, material con- 

 taining mature cercariae of Cryptocotyle which have emerged 

 from an infected Littorina kept over-night in a finger bowl. 

 To this add a drop of 1 : 1000 neutral red solution and cover. 

 As the cercariae become quiet look for the following: mouth, 

 pharynx, "penetration glands," tail fin, flame cells, excretory 

 vesicle, and germinal cells. 



Encystment of cercariae. — To a watch glass filled with 

 sea water, add first a piece of cunner fin and then several 

 mature cercariae. 



Observe and describe the activities of the cercariae dur- 

 ing encystment. 



Metacercariae. — Study and draw metacercariae of Cryp- 

 tocotyle as they appear when encysted in a cunner fin. 



Stunkard: The Life History of Cryptocotyle lingua (Creplin), with 

 Notes on the Physiology of the Metacercariae. Jour. Morph. and 

 Physiol., 50, 1930. 



CESTODA 



The Cestoda, or tapeworms, are endoparasites which pos- 

 sess very few of those organs that are characteristic of free- 



