28 Farmers’ Bulletin 1150. 
digests from the egg and releases an embryo, which is armed with six 
hooks. By means of these hooks the embryo cuts its way through 
the tissues of the sheep and into the blood stream. In the blood 
the embryos are carried to various tissues, but only those that 
reach the brain or spinal cord are able to attain the full larval de- 
velopment, the others dying and degenerating by the time they 
reach the size of a pea. Those that reach the central nervous sys- 
Fic. 18.—Gid parasite (Multiceps multiceps) from brain of sheep. Natural size. (From 
Hall, 1910.) 
tem at first move about on or in the brain or spinal cord, forming 
curving channels. At a suitable point the wandering ceases and 
the bladderworm grows and completes its development in about 
seven or eight months, the sheep dying in nine months or earlier. 
Distribution—In the United States this parasite has been found 
chiefly in northern Montana, where it has been established for about 
30 years, possibly longer. There have also been outbreaks of gid in 
Arizona and in New York. Cases have been observed also in various 
