q6 



Part second. 



secrete the two pieces of the shell. Tnis shell is like the binding 

 of a book, the leaves of which are represented by the two mantle- 

 flaps and four gill-plates. The cilia or hairs which cover the gills 

 and the mantle, by their beating movement create a current which 

 is constantly bringing fresh water from the surroundings to the 

 gills, so that the latter are well aerated. At the same time this 

 current serves to bring microscopic animals and other food material 

 into the mouth of the animal (see p. 58). Those mollusks which 

 burrow deep into the sand allow a pair of long tubes (siphons) 



Fig. 165. Solccurtus sirigilattis, ^2 ^^^- size, on the left the foot, 

 on the right the respiratory tubes. 



to protrude a little, and through these take in and pass out a 

 current of water (e. g. Solecurtus, fig. 165). — The Bivalves are 

 generally either fixed permanently like the oyster, or they burrow 

 to some depth into the sand; a very few can swim about freely 

 or can jump. 



We will commence the description of the Bivalves with the 

 Oyster — Honour to whom honour is due. Ostrea edulis (fig. 124) 

 is properly no aquarium-animal but, as all know, one for the 

 table, being much more attractive on the plate than behind glass 

 and more to be enjoyed with the tongue than the eyes. For its 

 exterior is modest, the shell flat and irregular and overgrown with 

 all sorts of animals and plants. But the rougher the shell, the 

 more tasty is the kernel, especially when covered with the white 

 hieroglyphics of Tube-worm borings. — The young oyster swims 

 freely for a short time only and then settles on rocks or wood, 

 cements its shell to the substratum, and gives itself up to the 

 task of cultivating a good taste and of producing millions of eggs 

 and sperm. It spawns in the summer months. 



The Oyster lives in all seas with the exception of the Baltic, 

 and often makes its way up into the rivers. In Europe and North 

 America they are artificially reared on "Oyster-beds", as they 

 are not only an article of luxury but (especially in England and 

 America) one of general consumption. The number of Oysters 

 eaten in England in a year is said to be 2000 millions, while America 

 consumes 4000 millions. Artificial culture was already practised 

 by the ancients; at the tables of Imperial Rome oysters were 

 never wanting, and epicures declared the best to come from the 

 Lake Lucrinus at Bajse. Brindisi, too, was one of the principal 



