PARASITES OF THE ALIMENTARY TRACT 87 
embryos, all of which are armed with three pairs of 
hooks. 
The embryo of each variety of tapeworm requires 
a special host, and in the event of being unable to 
find this it dies. When ingested, it is carried by the 
blood-stream to some organ, such as the liver, or even 
to the brain in some cases, and becomes encysted. The 
Dipylidium found in the dog is interesting, as the inter- 
mediate host is an invertebrate, as a louse or flea. 
The cysts just mentioned are not all alike. There are 
three varieties : Cysticercus, Coenurus, and Echinococcus. 
In Cysticercus the cyst has only one cavity, and con- 
tains only one head, or scolex, 
attached to its inner wall—z.e., 
it is monosomatic and mono- 
cephalic. 
In Coenurus the cyst is 
multilocular, and each loculus 
contains one scolex—i.e., it is 
polysomatic and monocephalic. 
In Echinococcus the cyst is 
multilocular, and each loculus 
contains several scolices—7.e., 
it is polysomatic and poly- : 
cephalic. Fic. 23.—T@nNia SERRATA: 
The whole cycle may take Hooxs. 
from two to eight months. 
Teenia Serrata.—This is one of the commonest tape- 
worms found in the dog. The length varies from 1 inch 
to 6 feet. The head is a little wider than the neck, 
and is armed with from thirty to forty hooks, which are 
of two classes, large and small. The latter possess a 
bifid guard. The segments are much longer than wide, 
and the posterior edges are widest, making a serrated 
edge. The genital pores are characteristic. They 
are arranged on alternate sides, and each is very 
