80 INVERTEBRATE ZOOLOGY 



CESTODA 



A TAPEWORM 



Tapeworms are common parasites in the intestines of ver- 

 tebrate animals. The human tapeworm, Taenia saginata, may 

 often be obtained from physicians. If it be alive when 

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

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

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

 alcohol or formalin. Taenia serrata, a tapeworm of the dog, 

 and Taenia crassieollis, which lives in the cat, are both common 

 animals 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, band-like objects, six inches or more in length, which are 

 attached by one end to the wall of the intestine. Care should 

 be taken in separating them from the intestinal wall 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 proglot- 

 tids, and the rounded knob, the scolex. The body of the ani- 

 mal 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; it, in fact, constitutes the entire 

 parasite when it first arrives in the intestine of the host (as 

 the animal is called in which a parasite lives), the proglottids 



