CLASS-BOOK OF ZOOLOGY. 163 



5 699. The greater part of them are carnivorous ; they 

 swallow other small animals or suck the juices of their bod- 

 ies. Only the land and soft-water shells are herbivorous. 



§ 700. This extensive order is divided into two families, 

 according to the number of their shells ; those with two 

 shells, as Muscles, and those with one shell, as Snails and 

 Cuttlefish. 



§701. The Muscle may be compared to a human body 

 without head, arms, or legs, and compressed on both 

 sides. To each side of the back is attached a pair of rib- 

 bon-like cross-barred gills, resembling a neck-ruffle ; 

 these, which are enveloped in the skin of the breast, and 

 called a cloak, are similar to a waist-coat, while around 

 them are situated two shells, like a jacket. On the in- 

 side of the cloak lies the wide mouth, surrounded by four 

 tri-cornered lobes, which are striped like the gills. From 

 one shoulder to the other runs a strong muscle, and a 

 second one between the two hips, which are fastened to 

 the shells, and effect their opening and closing. 



§ 702. The shell of the Stone-piercer (Pholas Dactylus) 

 is four inches long, with net-like stripes. It is found in 

 France and Italy, (principally in Trieste,) and in the 

 stone walls of the canals of the city of Venice. 



\ 703. The body of this animal is provided with several 

 moveable respiratory tubes, about the thickness of a finger, 

 and projecting from the shell. 



\ 704. The Stone-piercer is quite injurious, on account 

 of its boring passages in rocks, (even in the hardest 

 marble,) the stems of coral, oyster-shells, and the bottom 

 of ships. Its flesh excels in tenderness and delicacy the 

 oyster. 



\ 705. As the shell of this creature is very fragile, it is 

 obliged to seek for protection in a harder substance than 

 that of its own shell. The astonishing fact, that such a 

 weak worm is able to bore holes in a hard rock, may be 

 explained by that law of nature by which a very small 

 force, in constant action, produces more effect than a great 

 force, acting at intervals. This fact may illustrate our 

 application to mental pursuits. 



\ 706. The body of the Razor-shell (Solen) has a tubi- 



