Mollusca. S3 



Oyster. For several years also very large and good oysters have been 

 cultivated in take Fusaro. 



The Edible Mussel, Mytilus galloprovincialis (Fig. 25) , has the 

 well known almost triangular, blue-black shell. The animal has a so-called 

 byssus-gland with which it produces long horny threads, which fasten it 

 to rocks and woodwork. If it wants to leave its home , it produces a 

 new byssus with its finger-like foot and then it tears the old byssus away ; 

 by repeatedly doing this it moves very slowly onwards. It flourishes 

 best in northern seas , where it is extensively collected and cultivated ; 

 for this purpose trees are let down into the water and from time to time 

 drawn up, and the Mussels adhering are removed. 



Pinna (Fig. 1 28) is a large , thin-walled , club-shaped shell , which 

 is fixed in the mud by its narrow end. It also possesses a byssus which, 

 however, is much longer and composed of finer threads than that of the 

 Mussel. These silken threads were formerly used for the manufacture 

 of gloves, stockings and even entire garments : in the 18 th century there 

 existed at Naples and Sicily large works for spinning them. The shells 

 of Pinna also yield occasionally pearls, which, however, are of very little 

 value. The fable of the crab, Pinnotheres, acting as watchman to its 

 host, the Pinna, has been believed from the most ancient times up to 

 the present day ; similar crabs are known to frequent some other Mol- 

 lusks , Ascidians and Sponges. It is doubtful whether in any case the 

 host derives benefit from its lodger. 



Avicula i Fig. 129) is remarkable as a very near relation of Melea- 

 grina margaritifera , the Pearl-oyster , which produces the finest pearls. 

 These are nothing more than secretions of carbonate of lime with which 

 the animal covers up extraneous bodies (mostly a parasitic worm), which 

 irritate its body. Each pearl contains at its centre some such object, and 

 in this way man can cause the production of pearls, a fact of which the 

 Chinese have taken advantage to make pearls of various forms. 



A shell of interesting habits is Lithodomus (Fig. 27) , which is 

 always found in holes, in rocks or coral reefs. The animal is a favorite 

 delicacy and often appears in the markets. It is not yet understood how 

 it works its way into the stone : its shell is perfectly smooth and so it 

 cannot file its way in, as the Piddock, Pholas (Fig. 26), does with its 

 rough shell armed with hard ridges : probably Lithodomus secretes a fluid 

 which acts upon the limestone and dissolves it. The holes they make are 

 quite smooth inside. 



The Temple of Serapis at PozzuoK has made these shells of in- 

 terest , as its columns have a zone 6 feet high marked with the holes 

 formed by these shells. It is hence concluded that the temple must 

 have sunk under the level of the sea for a time and then been raised 

 again. 



Deeply buried in the sand may be found the Razor-shells, Solen 

 Fig. 171) and SolecurtUS (Fig. 170j , which are sought after as deli- 

 cacies. They are sold on the market with other edible shells as Fruits 

 of the Sea (Frutti di mare, and are eaten raw. 



While all the above named bivalves afford examples of the still-life 

 of the ocean, the Cockle and Scallop are by no means slow of movement. 



