190 



UN ZOOLOGICAL SYSTEMS, AND THE 



orawl on their bellies, and carry the shell over them as a shield. They 

 have a distinct and moveable head, by which they essentially differ from 

 our next order, vjrhich are without a distinct head of any kind. The two 

 sexes are united in the same individual, but require a reciprocal union for 

 breeding. 



The BivALVED or two-shelled testaceous wokms, the acephala or 

 headless of Cuvier, are best explained by referring you to the oyster and the 

 muscle, (ostrea and mytilus,) both which contain species that produce 

 pearls, and mother of pearl. Though the real peaa-l-muscle is amya or 

 gaper, found chiefly on the coasts of Malabar and Ceylon, where the prin- 

 cipal pearl-fisheries are established. The species of oyster that produces 

 small pearls is sometimes traced on our own shores, and is said to have 

 been at one time frequent in the river Conway, in Wales. Most of the 

 oysters cast their spawn towards the close of the spring, or in the begin- 

 ning of the summer, as the month of May. This spawn is by the fisher- 

 men called SPAT, and in size and figure each resembles' the drop of a 

 candle. As soon as cast or thrown off*, these embryon disks adhere to 

 stones, old oyster-shells, pieces of wood, or whatever other substance 

 comes in their way ; a calcareous secretion issues from the surface of their 

 bodies, and in the course of twenty-four hours begins to be converted into 

 a shelly substance. It is two or three years, however, before they acquire 

 their full size. 



The scallops, which are a tribe belonging to the oyster kind, are capable 

 of leaping out of the water at pleasure, to the distance of half a yard : when 

 ^evated they open their shells, and eject the water within them, and then 

 falling back into the water close them with a loud snap. 



Among the more elegant of this division, is the nacre, pinna, or sea.-pen, 

 so called from its form ; the animal of which, (a lamix or slug) secretes, as 

 we have already observed, a large quantity of fine strong silky hair, or beard, 

 which by the Italians is woven into a kind of silky plait. And among the 

 most extraordinary is the gigantic chama or clamp-shell, in form resembling 

 the oyster : one species of which we noticed not long since, as found in the 

 Indian ocean, of the weight of between five and six hundred pounds ; the 

 fish or inhabitant large enough to furnish a hundred and twenty men with a 

 full meal, and strong enough to lop oflT a man's hand, and cut asunder the 

 cable of a large ship. 



Of the MULTivALVED TESTACEOUS WORMS, or thosc Containing more than 

 two shells, there are but three known species, the chiton, the lepas or acorn- 

 shell, and the phloas, or as it is often improperly called phoias, so de- 

 nominated from its secreting a phosphorescent liquor of great briUiancy, 

 which illuminates whatever it touches or happens to fall upon, and to 

 which Linneus chiefly ascribed the luminous appearance which the sea 

 often assumes at a distance : a subject, however, which we shall have oc- 

 casion to examine hereafter. 



The FOURTH ORDER of the Linnean class of worms is called zoophytes, 

 or PLANT-ANIMALS, SO denominated from their efflorescing like plants. 

 Most of them are of a soft texture, as the hydra or polype, so well known 

 from its being capable of existing when turned inside out, and of reprodu- 

 cing any part of its tentacles or body when destroyed by accident. Some are 

 corky or leathery, as different species of the alcyonium ; some bibulous, as 

 the spongia or sponge, which is now decidedly ascertained to be an animal 

 substance : and some calcareous, as the numerous families of coral, which. 



