Which is the only living pa of Hydatid cyst?

Hydatid cyst is caused by Echinococcus granulosus. It has a thick opaque white outer cuticle / laminated layer and an inner thin germinal layer containing nucleated cells. The germinal layer is the site of asexual reproduction. It also secretes the hydatid fluid which fills the cavity. The fluid is clear, colourless / pale yellow with a pH of 6.7 containing salts and protein. It is a good antigen which sensitises the host. The fluid was used as the antigen for Casoni's intradermal test and other diagnostic serological tests. From the germinal layer, small knob like excrescences / gemmules protrude into the lumen of the cyst. These enlarge and become vacuolated and filled with fluid. These are called brood capsules. They are initially attached to the germinal layer by a stalk, but later escapes free into the fluid filled cyst cavity. From the inner wall of brood capsule, protoscolices develop, which represent head of adult worm, complete with invaginated scolex, bearing suckers and hooklets. Each of these are potential tapeworm. Many of the scolices float free in the cyst fluid. These with free brood capsules are called hydatid sand. Ref: Paniker's Textbook of parasitology, 6th Ed page 151.