136 



ANIMAL PARASITES AND MESSMATES. 



mentions, among others, a species belonging to the 

 muscidae, the Limosina luguhris, which does not measure 

 a Hne in length, and which harbours as many as fifteen 

 pteropti under its abdomen. 



Bees, which give us their wax and their honey in 

 exchange for the shelter which we afford them, have a 

 mortal enemy, an acarus, which attaches itself to them, 

 not in order to gain any advantage from them, but to 

 cause their death. It is not so much a parasite as an 

 assassin, and we may be excused from describing it. We 

 have found acaridse on certain polyps, the Campanulariae 

 and Sertularise of our coasts, and some years ago we 

 described one which is very curious, and inhabits the 

 southern whale, in the midst of its Cyami and Tubi- 

 cinellae. The anodonts of our ponds, as well as the 



Fig. 24.-Hydrachna geographica. 



Uniones usually have the skin of their feet and that of 

 their mantle encrusted with acari of every age, to which 

 the name of Atax ypsilopJiora has been given. The 

 species which live on the anodonts are not the same as 

 those which inhabit the Uniones ; and Mons. E. Bessels, 

 who has so fortunately returned from his voyage to the 



