ANIMAL PARASITES AND MESSMATES. 



CHAPTEE II. 



FREE MESSMATES. 



We meet with free messmates in various classes of 

 the animal kingdom. They sometimes mount on the 

 back of a neighbour, sometimes occui)y the opening of 

 the mouth, the digestive passages, or the exit for the 

 excreta; at times they place themselves under the 

 shelter of the cloak of their host, from whom they 

 receive both aid and protection. 



Among the vertebrates, there are few except fishes 

 which merit a place here ; it is only amongst these that 

 we meet with s]3ecies at the mercy of others, and 

 dependent on acolytes, which are in every respect 

 inferior to themselves. 



An interesting messmate belonging to this first 

 category is a fish of graceful form, named donzelina, 

 which goes to seek its fortune in the body of a holo- 

 thuria. Naturalists have long known it under the name 

 of Fierasfer. It has a long body like that of an eel, 

 entirely covered with small scales ; and as it is quite 

 compressed, it has been compared to the sword which 

 conjurors thrust into their oesophagus. They are found 

 in different seas, and all have similar habits. This fish 

 is lodged in the digestive tube of his companion, and, 



