10 
BULLETIX 260, U. S. DEPARTMENT OF AGRICULTURE. 
may attain a length of 2 or 3 feet. In the terminal segments are 
eggs, and these segments with the contained eggs pass out in the. 
feces of the dog and contaminate vegetation, soil, and water. Such 
herbivorous animals as sheep, which graze over range or pasture 
contaminated in this way. pick up these eggs as they feed and swal- 
low them. In the stomach of the sheep the shell is digested and 
the small, hooked embryo released. The embryo bores its way 
through the wall of the digestive tract and into the blood vessels 
and is carried around until it lodges 
somewhere. Embryos which do not 
lodge in the central nervous system 
start to grow, but very soon perish. 
Very commonly, however, the para- 
site makes its way to the central 
nervous system, lodging as a rule in 
the brain, though it occasionally oc- 
curs hi the spinal cord. In the brain 
the embryo grows to form the blad- 
der worm or ccenurus. and this may 
attain the size of an egg. or even a 
larger size. As it grows it presses 
upon the adjacent portion of the 
brain and destroys it. The pressure 
and the irritation, due to the hooks 
with which the tapeworm heads of 
the ccenurus are provided, cause very 
distinctive symptoms, the sheep com- 
monly holding its head in an odd 
position and walking in a circle 
toward one side or the other. Un- 
less the ccenurus is removed by oper- 
ation the sheep invariably dies. 
When the brain of such a sheep is 
eaten by dogs — and dogs very read- 
ily eat the brains of sheep by licking 
them out through the large opening 
at the base of the skull — the coenurus is ingested with the brains 
and the tapeworm heads pass to the intestines of the dog and give 
rise to the adult tapeworms. As in the case of the hydatid, the gid 
parasite must always be transmitted from the dog to other animals 
which eat the eggs from the dog tapeworm, and from the other ani- 
mals to the dog by the dog eating the brain or at least the ccenurus 
from the brain of a °iddv animal. 
Fig. 5. — Adult gid tapeworm from the 
dog. Natural size. (Specimen No. 
4031, Bureau of Animal Industry 
helminthological collection.) 
