Tapeworm. Light micrograph of a dog tapeworm, Echinococcus granulosus, which also infects humans to cause hydatid cysts. In canines, the tapeworm develops into the adult form seen here, attaching itself to the intestinal wall with the head-like scolex (at lower left). The tapeworm produces eggs which pass out with the feces. If these are ingested by humans or herbivores, the eggs hatch and penetrate the intestinal walls. They migrate to the liver, lungs, brain and bones. Here they form slow-growing, tumor-like hydatid cysts. Symptoms appear 5-20 years after infection and include pains and damage to the surrounding tissue by the cyst. Magnification: x40 at 35mm size.