68 ANIMAL PARASITES AND MESSMATES. 



CHAPTER IV. 



MUTUALISTS. 



In this chapter we bring together animals which live on 

 each other, without being either parasites or messmates ; 

 many of them are towed along by others ; some render 

 each other mutual services, others again take advantage 

 of some assistance which their companions can give 

 them ; some afford each other an asylum, and some are 

 found which have sympathetic bonds which always draw 

 them together. They are usually confounded with para- 

 sites or messmates. 



Many insects shelter themselves in the fur of the 

 mammalia, or in the down of birds, and remove from 

 the hair and the feathers the pellicle and epidermal debris 

 which encumber them. At the same time they minister 

 to the outward appearance of their host, and are of great 

 utility to him in a hygienic point of view. 



Those which live in the water have other guardians : 

 instead of insects, we find a number of crustaceans 

 which establish themselves on fishes, and if there are 

 no scales of the epidermis which annoy them, there 

 are mucosities which are incessantly renewed in order 

 to protect the skin from the continual action of the 

 water. 



