OF BIVALVED SHELL-FISH; 255 



As the land fnail, being beft known, took the lead in the fornfier clafs, 

 for the fame reafonthe frefli-water mulTei may take the lead in this. 



The muffel of frefli or fait water has two equal Ihells, joined at the 

 back by a ftrong mufcular ligament that ferves as a hinge. The animal 

 can open its fhells, at pleafure, about a quarter of an inch. It is fixed to 

 each Ihell by four tendons, which fhut them clofe, and keep its body 

 firm fi-om being crufhed by any fhock againfl: its own habitation. Its 

 vital organs are fituated in a very extraordinary manner. It has a- 

 mouth furniihed with two flelhy lips ; its inteftine begins at the bottom 

 of the mouth, pafies through the brain, and makes a number of circum- 

 volutions through the liver ; then goes on ftraight into the heart, which 

 it penetrates, and ends in the anus j near which the lungs are placed, and 

 through which it breathes, like thofe of the fnail kind; and in this manner 

 its languid circulation is thought to be carried on. Each muflel has two 

 ovaries, by which it is female ; and two feminal veflels, as a male. 

 Each has its own proper canal : by the ovary canal the eggs defcend to 

 the anus ; where the feminal canals fend their fluids to impregnate ' 

 them. Thus one fingle animal fuffices for generation j and the eggs arc 

 impregnated and excluded by itfelf alone. The ovaries ufually empty 

 themfelves of eggs in fpring, and are replenifhed in autumn. The fe- 

 cundity of the fnail kind is trifling in comparifon to the fertility of thefe. 

 Their quick multiplication alone infures the continuation of their fpecies. 

 The multitude of thefe animals in fome places is very great ; but the 

 numbers of their deftroyers are in equal proportion. The crab, the 

 cray-fifh, and many other animals, devour them ; and the trochus is 

 their moft formidable enemy. But it feems ftill more fearful of the 

 agitations of the element in which it refides j for if daflied againfl rocks, 

 or thrown far on the beach, it is inevitably deftroyed. To guard againft 

 this, the moft fatal of accidents, it is furniflied with a capacity of binding 

 itfelf by a number ofthreads to whateverobjedl it approaches: thefe Reaumur 

 fuppofed it fpun artificially, as fpiders their webs; but the extreme 

 length of this beard in fome, which far exceeds that of the body, feems 

 impoflible to be manufaftured by thrufting out and drawing in the 

 tongue, with the glutinous matter of which the French philofopher fup- 

 pofed thofe threads were formed. It alfo increafes with the animal ; and, 

 as the muflel becomes larger and older, the beard becomes longer, and 

 its filaments ftronger. By thefe threads they adhere to fixed objefls ; 

 and fometimes, when fuch are wanting, to each other ; and though thrown 

 into a lake feparately, they are taken out in bunches of many together. 



U u 2 Its 



