TRANSMIGRATIONS AND METAMORPHOSES. 207 



besides those which they lodge for the sake of the car- 

 nivora. The worms of the herbivora have particular 

 characters by which they are easily known ; they have 

 no crown of hooks. 



The taenia of the wolf, which has often been con- 

 founded with the Twiiia serrata, lives in the brain of 

 the sheep, and produces a disease known as the ''gid." 

 It was formerly said that every animal has its enemy. 

 We should rather say that each species has its parasites, 

 and each parasite has its vehicle by which it is intro- 

 duced. 



These tape -worms are found in all the vertebrate 

 classes. An herbivorous animal usually serves as a 

 vehicle, but it more fi-equently carries, besides its 

 passengers, species which are peculiar to itself. As 

 the carnivorous animal is not intended to be eaten 

 like the herbivora, it cannot serve as a vehicle, and if by 

 chance its muscles enclose some passenger, he has lost 

 his way and that for ever. 



Do the cetacea generally live on fish, and do they 

 become the prey of some aquatic carnivora ? We have 

 reason to think so, from the presence of certain agamous 

 cestodes, which have been frequently found in too great 

 number to allow us to suppose that they have lost then- 

 way in these aquatic mammals. There have been seen 

 in the substance of the muscles of many species, or 

 rather in the layer of blubber which covers the skin, 

 agamous cestode worms of the genus Phyllohothrium, 

 which can only accomplish their evolution in some large 

 squahis. There must then be contests between dolphins 

 and sharks, contests in which the dolphins are worsted, 

 in spite of then* superiority. These Phyllobothria have 



