Hepatic fibrotic foci indicative of embryonic cysticerci first appeared in lambs with 7-day infections, and macroscopic cysticerci (1 to 9 mm.), most within haemorrhagic streaks, occurred at 10 days. Migration of cysticerci into the abdominal cavity from streaks and open pits in the liver capsule occurred in 18- to 25-day infections, and from the omentum in 25- and 30-day infections. Cysticerci in the abdominal fluid were last observed at 43 days. Most cysticerci that remained within the liver parenchyma of lambs became entombed within caseous and fibrotic matter, and failed to complete their rostellar development irrespective of the period of infection. Those at other sites developed suckers and complete hooks between 34 and 53 days. Cysticerci within the parenchyma of a moose completed their development. Hyalinosis of some omental cysts in lambs occurred at 25 days, but the cysticerci within remained viable until at least 53 days when some were infiltrated with caseous matter. A fibroma was associated with an omental cyst. Crystallized flakes occurred in teased hepatic haemorrhagic streaks and omental cysts in 4-month infections. Cysts displayed subsequent size regression. Adhesions and ribbons of fibrotic tissue, most involving the liver and diaphragm or the omentum and body wall, occurred initially in infections of 30 and 61 days respectively.In infections longer than 53 days, the number of viable or degenerate cysticerci in lambs and swine at sites exclusive of the liver parenchyma was proportional to the total number of cysts. The increment in the size of these viable cysticerci increased at the same rate both before and after complete rostellar development. Only cysticerci with complete rostellar hooks infected dogs. Prepatent periods in dogs spanned about 2 months, and strobilar longevity varied from [Formula: see text] to at least [Formula: see text] months.