WORMS. 



181 



tail and changes into the adult fluke, which makes its 

 way into the liver. In other cases the change is from snail 

 to birds or to frogs, the host of the immature forms being 

 usually a mollusc, that of the adult a vertebrate. 



ORDER III. CESTODA (Tapeworms). 



The Cestodes are all parasitic in other animals. They 

 differ from the Trematodes in the complete absence of 

 mouth and digestive tract, since they absorb their nourish- 

 ment through the skin. Usually they have ribbon-like 

 bodies, and hence are commonly known as tapeworms 

 (fig. 26). At the anterior end are 

 the means of attachment (hooks or 

 suckers) by which the animal at- 

 taches itself to the lining of the intes- 

 tine of its host, while usually the 

 body becomes broken up into a series 

 of joints or proglottids. There is con- 

 tinually a formation of new proglot- 

 tids near the 'head.' or scolex, while 

 the older proglottids, loaded with 

 eggs, drop off and are carried out 

 with the waste of the digestive 

 tract. These tapeworms obtain en- 

 trance into the boclv in the food, 



*/ 



man usually receiving his from raw or FJG 

 partially cooked beef or pork, and 

 more rarely from fish. The proglot- 

 tids and eggs, passing from the body, 

 may fall where they may be eaten by cattle or swine. 

 Inside their bodies they undergo partial development in 

 the muscles, and then when taken into the human body 

 they complete their development. Other vertebrates than 

 man possess tapeworms. The cat gets hers from the mouse, 



Tapeworm 

 ( TII n ia ) with proglottids 

 from different regions of 

 the body, h, head en- 

 larged. 



