NATURAL HISTORY. 



and while stopping with the Natchez tribe made the following observa- 

 tions: ■' There is a great many divers of that nation, who dive to the 

 bottom of the water and fetch up these precious shells from the lowermost 

 pari of the rocks. On a fair day you may see the shells on the rocks 

 open themselves to receive the dew of heaven, which dew breeds the 

 Him seeds of the pearl within the shells, which appear like little white 

 grain that si irks fast to the shell. These small, soft . grains do in time 

 become hard and white, as we see they are. It is observed that the pearls 

 which are fetched from the bottom of the sea are fairer than those which 

 are found on the rocks, because the sun tarnishes these, and the thunder is 

 destructive to their seeds." 



Of the fresh-water mussels there are some twelve hundred so-called 

 species scattered in all parts of the world; but nowhere are species and 

 specimens so abundant as in the limits of the United States. Indeed, we 

 have so many that naturalists have gone crazy over them, and described 

 species after species upon the slightest variation in shape or color, until it 

 seems as if every stream and pond — yes, almost every mud-puddle — must 

 have • species' peculiar to it. Yet, notwithstanding all this abundance of 

 individuals and superabundance of species, notwithstanding good old Dr. 

 Lea's thirteen ponderous volumes of "Observations on the Genus Unio," it 

 would seem as if no other group of molluscs could be of as little value to 

 man as this. Aside from its producing pearls and the occasional use of 

 its valves f«u' spoons by campers-out, the fresh-water mussel is useless. Its 

 flesh is of no value, while it does not feed on forms injurious to human 

 interests. It lives a lazy life, slowly ploughing through the gravel in the 

 bottoms of rivers or the mud in the bottom of ponds, swallowing micro- 

 scopic forms for food, and at the suitable time hatching- out its half a 

 million, or even two million, young. 



These young, however, have a history which is interesting, since it fur- 

 nishes almost the sole example of parasitism among the Acephals. When 



it escapes from the parent, the young fresh-water 

 mussel differs extremely from the adult. It has 

 a bivalve shell, as has the parent ; but here the 

 resemblance ends, for the shell bears on the free 

 edge of either valve a strong, toothed hook. 

 These embryos swim about through the water 

 ^t^7^SiS^^S}SSw. imtil the y come in contact with a fish, the pres- 

 Slf?to h fishe S s bywhichita " aches ence of which they are able to recognize by 



means of peculiar sense-organs, which subse- 

 quently become lost. Then the valves close together, and the hooks serve 

 i an anchor, holding the embryo fast to the skin of the fish. Here it 



