There are two forms of hydatid cyst which show themselves in the human liver. The more common one is the Echinococcus cysticus; the rare one is the Echinococcus alveolaris. The life history of the Echinococcus cysticus has been very fully studied by Leuckart, and further studies may be consulted in Bulletin 19 of the Bureau of Animal Industries of the United States Department of Agriculture, published in 1898.
LIFE HISTORY OF THE PARASITE.
The position of the echinococcus cyst in the life history of the animal is extremely interesting. A tapeworm (Fig. 1) only 1.5 to 3.0 mm. long, which infests the intestinal tract of the dog and other canidæ, deposits its eggs by millions with the excreta. By natural processes the eggs are washed out of the excreta and fall on vegetation, which sooner or later becomes the food of man or other intermediary host, mostly