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ANIMAL PARASITES AND MESSMATES. 



CHAPTEE VIII. 



PARASITES THAT ARE FREE WHEN OLD. 



We are about to study in this chapter animals "which 

 seek for assistance from others while young, and are able 

 to provide for themselves completely when they have 

 grown old. We may compare the hosts which afford 

 them shelter to creches which receive none except new- 

 born infants. It is generally supposed that animals 

 known under the name of parasites are such as require 

 assistance from their neighbours during all the stages of 

 their existence.* This is a mistake. There are very few 

 among them which are not able to provide for themselves 

 during some period of their development, and they then 

 lead an independent life. We have mentioned a certain 

 number of them in the preceding chapter, which only 

 seek for external assistance when they are old ; we bring 

 together, on the contrary, in this chapter, those which 

 require help at the commencement of their life, and live 

 at large on their own industry when they have once made 

 their entry into the world. There are even some among 



* The discovery of a free bothriocephalus at the bottom of a ditch 

 caused a great sensation in the world of naturalists some years ago. It 

 was then thought that the parasite could not exist except in the body of 

 an animal : they could only imagine it shut up as in the cells of a gaol. 



