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 0.75% 
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 erassicollis, 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 
