There exists a singular cestode which bears the name of _Echinococcus_. We give a figure of the echinococcus of the pig, slightly magnified, and an isolated scolex (Figs. 55 and 56). In its first form it is composed of closed sacs, which grow to the size of a nut, and sometimes to that of an orange. It usually lodges in the liver of the pig, but establishes itself also in man. We have been assured that part of the population of Iceland have been attacked by it. The abundance of this parasite in that country is attributed to the want of cleanliness, and the number of dogs that they keep around them. The echinococcus becomes a tænia in this animal. It scatters the eggs with its dung, leaving them directly or indirectly on plants which the Icelanders eat; for they gather for food certain mosses, 226 sorrel, cochlearia, dandelion, &c., from the midst of the plains in which live flocks of sheep guarded by dogs. The eggs are scattered everywhere on plants or in the water. [Illustration: Fig. 55.--Isolated scolex of the _Tænia echinococcus_ from the pig.] [Illustration: Fig. 56.--_Tænia echinococcus_, from the pig.] Leuckart has made some very interesting experiments on the echinococci. In Fig. 57 is shown a tænia which proceeds from an echinococcus. [Illustration: Fig. 57.--_Tænia echinococcus_, from the dog.] [Illustration: Fig. 58.--Bothriocephalus latus. _a_, scolex, _b_, the proglottides, _c_, the sexual organs.] There is yet another tape-worm harboured by man, the _Tænia lata_, better known under the name of Bothriocephalus. We give in Figs. 58, 227 59, and 60 representations of this worm in the state of a colony, also the scolex or head separately, and an egg. Its history is very curious, especially with reference to its geographical distribution. It is only found in Russia, Poland, and Switzerland, and the limits 228 of the places which it inhabits are perfectly defined. Siebold, during his stay at Königsberg, could determine from the nature of the worms, whether the patient who consulted him lived on one side or the other of the Vistula. [Illustration: Fig. 59.--Bothriocephalus latus, scolex.] [Illustration: Fig. 60.--Bothriocephalus latus, egg.] A Russian naturalist, Dr. Koch, thoroughly studied this interesting worm and its evolution. He says that this cestode is rare at Moscow, while at St. Petersburg, Riga, or Dorpat it is common. If this be really the case, it must doubtless be attributed to the fact that in one place the inhabitants drink spring water, and in the other water from the river.