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CHAPTER III. 



FIXED MESSMATES. 



The animals ' of which we have just spoken usually 

 preserve their full and entire independence; from the 

 time of their leaving the egg, till their complete develop- 

 ment, they are subject to no other outward changes than 

 such as belong to their class. If they sometimes renomice 

 their liberty, it is only for a limited time ; and they all 

 preserve not only their peculiar appearance, but their 

 organs intended for fishing or for locomotion. It is not 

 thus with those which we are now about to consider ; 

 they are free in their youth, but as they draw near to 

 puberty they make choice of a host, instal themselves 

 within him, and completely lose their former appear- 

 ance : not only do they throw aside their oars and their 

 pincers, but they cease sometimes to keep up any com- 

 munication with the outer world, and even give up the 

 most precious organs of animal life, not even excepting 

 those of the senses ; iliej are installed for life, and their 

 fate is bound up with the host which gives them shelter. 

 The number of these messmates is considerable. 



We shall first allude to some crustaceans named 

 Cirrhipedes by Lamarck. The metamorphoses which 

 they have undergone since they left the egg have so 



