24. Farmers’ Bulletin 1150. 
. BLADDERWORMS. 
THE THIN-NECKED BLADDERWORM.2° 
Location.—The thin-necked bladderworm is found in the abdomi- 
nal cavity attached to the mesenteries or omenta or in the liver. 
Appearance.—The bladderworm looks like a sac full of a clear 
fluid, with a white object, which is the head and neck, projecting into 
it from one end. It is usually about 1 inch in diameter, but may 
attain a long diameter of several inches. The bladderworm proper 
is surrounded by a cyst, which is developed by the host animal as a 
protective measure against the parasite. When this cyst is broken 
the parasite usually rolls out and is seen to be a thin-walled structure. 
By careful manipulation the head and its rather long neck may be 
squeezed out at one end of the “bladder” 
(fig. 15). 
Life history.—If one or these bladderworms 
is fed to a dog the cyst wall will digest, but the 
tapeworm head and neck will pass on to the 
small intestine of the dog and begin to grow 
segments back of the neck. In this way it will 
form a tapeworm, one of the largest of the dog 
tapeworms ™ (fig. 16). Thistapeworm attains 
BIG mn Wnnot* a length of a yard or more, becoming mature 
erworm (Cysticercus 
tenuicollis). Natural size. and beginning to liberate egg-bearing seg- 
zo Sullesy Anes) ments in the course of 10 or 12 weeks. When 
dogs infested with these tapeworms run over pastures used by sheep, 
they leave feces containing the tapeworm eggs on the pastures, and 
these eggs are spread by rain and washed on to the grass and into 
streams and puddles where the sheep drink. When the sheep get these 
eggs in food or water, the embryo escapes from its surrounding shell, 
makes its way to the liver of the sheep, and begins to develop. In 
time it slips out of the liver and becomes attached to the mesenteries 
or omenta. At first it is a bladder without a head, but later the head 
and neck develop, and it is then ready to infect any dog that eats it. 
Distribution —This parasite is quite generally distributed over the 
United States, but the indications are that the worm is becoming 
less common as a result of improvements in disposal of viscera and 
offal at slaughterhouses during the last 15 years. It is most likely 
to be present where sheep are associated with dogs, either when 
herded by them or where stray dogs are common, and where sheep 
are slaughtered on farms or at small country slaughterhouses at 
10 Cysticercus tenwicollis. 
1 Commonly called Tenia marginata, and more properly Tenia hydatigena. 
