TRANSMIGRATIONS AND METAMORPHOSES. 225 



vain to distinguish these worms from each other by their 

 hooks. The wolf or the dog follows the flock of sheep, 

 scatters the proglottides or the eggs in their way, and the 

 sheep, browsing on the grass with the eggs attached, 

 become infested with their most dangerous enemy. 



To arrest this disease, only one thing is necessary, to 

 destroy by fire the head of every sheep attacked by the 

 " gid." The rest of the animal may be eaten without 

 danger. 



Pouchet did not succeed in giving sheep the "gid" at 

 first, for the very simple reason that he employed the 

 eggs of the Teenia serrata, instead of those of the Tsenia 

 coenurus ; he had confounded the two species. The 

 ccenurus of the sheep is a true calamity when it spreads 

 in a country. The animal attacked by it is lost, and the 

 mischief may be indefinitely propagated by giving aB food 

 to dogs the head of the sick animal, with thousands of 

 young taeniae enclosed within each. 



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 some- 

 times 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 tsenia 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 



