A TAPEWORM 65 



Class : Cestodes 

 A TAPEWORM 



Tapeworms are common parasites in the intestines of ver- 

 tebrate animals. Tcenia saginata, the common tapeworm infest- 

 ing man, may often be obtained from physicians. If it is alive 

 when obtained, it should be placed in a normal salt solution (a 0.75 

 per cent solution), in which it will keep alive for several hours, 

 and may then be studied. If it is dead it should be preserved in 

 alcohol or formalin. Tcenia serrata, a tapeworm of the dog, and 

 TcBuia crassicollis, which lives in the cat, are both common ani- 

 mals and are convenient forms for study. The intestines of adult 

 cats or dogs should be slit open and the worms taken out and 

 placed alive in a normal salt solution. They are white, bandlike 

 objects, six inches or more in length, which are attached by one 

 end to the wall of the intestine. In separating them from the 

 intestinal wall care should be taken not to tear them. 



Study the movements and general form of the animals as they 

 lie in the salt solution. The worm will be seen to be made up of a 

 large number of segments, and to bear at the smaller end a small 

 rounded knob. The segments are called proglottids, and the 

 rounded knob, the scolex. The body of the animal is not made 

 up of body divisions which we can call head and trunk. The 

 scolex, however, may be held to represent its anterior end, the 

 proglottids having arisen from it by a process of terminal growth. 

 The scolex is thus the oldest part of the animal's body ; in fact, 

 it constitutes the entire parasite when it first arrives in the in- 

 testine of the host (as the animal is called in which a parasite 

 lives), the proglottids only then beginning to grow. The youngest 

 proglottids are those nearest the scolex; those at the opposite 

 end of the body are the oldest and hence the largest. Count the 

 proglottids. The animal attaches itself to the wall of the intestine 

 by means of its scolex, which is provided for this purpose with 

 four suckers and usually two rows of chitinous hooks ; the scolex 

 of TcBnia saginata lacks the hooks. Thus attached, it lies im- 

 mersed in the digestive fluids of its host and absorbs through the 



