Fig. 123.—Portion of the intestine of a dog infested with the adult hydatid tapeworm (Tænia echinococcus) natural size. (After Ostertag, 1895.)
Fig. 124.—Adult hydatid tapeworm (Tænia echinococcus) enlarged. (After Leuckart, 1880.)
Fig. 125.—Hooks of adult hydatid tapeworm. a, From a hydatid; b, three weeks after feeding to a dog; c, from an adult; d, combined figures of a-c, showing the gradual changes in form. × 600. (After Leuckart, 1880.)
Life history. Starting with the adult tapeworm (Fig. 124) in the small intestine of the dog or wolf, the eggs are scattered over the ground and are swallowed by the intermediate host with the fodder or water. Upon arriving in the stomach the egg-shell is destroyed, and the six-hooked embryo, which is thus freed, bores its way through the intestinal wall, and wanders, actively or passively (that is, carried along by the blood), to various organs of the body—liver, lungs, ovaries, bones, skull, etc.—where it develops first into an acephalocyst, which may develop further, as shown by the accompanying illustrations. The heads which are formed, upon being devoured by a dog or wolf, then develop into adult tapeworms.
Young animals are most exposed to this disease; in adults or aged animals the migration and development of the embryo are more difficult.
Fig. 126.—Diagram of an echinococcus hydatid. cu, Thick external cuticle; pa, parenchym (germinal) layer; c, d, e, development of the heads, according to Leuckart; f, g, h, i, k, development of the heads according to Moniez; l, fully-developed brood capsule with heads; m, the brood capsule has ruptured, and the heads hang into the lumen of hydatid; n, liberated head floating in the hydatid; o, p, q, r, s, mode of formation of secondary exogenous daughter cyst; t, daughter cyst with one endogenous and one exogenous granddaughter cyst; u, v, x, formation of endogenous cyst, after Kuhn and Davaine; y, z, formation of endogenous daughter cysts, after Naunyn and Leuckart; y, at the expense of a head, z, from a brood capsule; evag, constricted portion of the mother cyst. (After R. Blanchard, 1886.)