THE OYSTER AND ITS RELATIVES. 



Of all the grand divisions of the Animal 

 Kingdom, the subkingdom MoUusca is 

 probably the least known to the ordinary 

 observer, and if one were asked to enu- 

 merate as many different kinds of "shell 

 fish" as he could, it is probable that not 

 over six or eight different varieties would 

 be named. The majority of people think 

 of a clam, oyster, mussel, snail or Nautilus 

 and their molluscan vocabulary ends with 

 these names. And yet this group of ani- 

 mals is second only to the insects in num- 

 ber of different species, beauty of colora- 

 tion and interest of habitat. They may be 

 found everywhere, in salt and fresh water, 

 in our forests and fields, our ponds, 

 brooks and rivers ; in the valleys and on 

 the mountain tops, and even in the waters 

 of the frozen north, while in the warm 

 waters of the tropics they flourish in un- 

 counted millions. In size they range from 

 the little sea-snails hidden in the eel grass 

 along the shore, with tiny shells scarcely 

 an eighth of an inch in length, to the 

 giant squid, which measures forty feet 

 or more from the tip of its tail to the end 

 of its long arms ; and they range from the 

 tide-washed beach to the abyssal depths 

 of the ocean. It is to these lowly crea- 

 tures that I would draw the reader's at- 

 tention. 



In nearly all the species of the Mollusca 

 the animal is protected by a hard shell, 

 made of carbonate of lime, which is cov- 

 ered with a horny epidermis to protect 

 the limy shell from being dissolved by 

 the acids in the water. This shell is gen- 

 erally capable of containing the entire 

 animal, thus affording, in most cases, ad- 

 equate protection for the soft body. 

 Those animals not provided with a shell, 

 as is the case with the land slugs, are ca- 

 pable of covering themselves with a sort 

 of mucus which encysts and protects 

 tliem from both extreme heat and cold. 



The lowest branch of Mollusca is 

 known as class Pelecypoda, which com- 

 prises all of the different kinds of clams, 

 mussels, quahaugs, etc., in which the 

 body is protected by two hard, calcareous 

 shells placed, generally, opposite each 

 other and connected on the upper mar- 

 gin by a ligament, and the two valves 

 work back and forth in teeth and sockets, 

 making a kind of hinge. A set of stout 

 adductor muscles keep the two shells or 

 valves together and allow them to open 

 and close at the will of the animal. The 

 majority of clams live in the mud in a 

 horizontal position, the anterior end be- 

 ing buried and the posterior end, con- 

 taining the siphons which draw in and ex- 

 pel the water, being out of the mud, in the 

 water. The clam progresses by pushing 

 forward its strong, muscular foot, getting 

 a firm hold of the mud and then drawing 

 the shell after it. Some pelecypods, as 

 the oyster, live attached to some object 

 on the bottom of the water, as a stone, 

 piece of wood or piling of an old wharf, 

 and are not able to travel from place to 

 place as are the true clams, examples of 

 the latter being fresh water mussels and 

 the marine quahaug or round clam. 



Some bivalves also attach themselves 

 by a byssus composed of a number of 

 silk-like threads, which anchor their 

 shells to stones, sticks^ and other foreign 

 objects. In one group (genus Pinna) 

 found in the Mediterranean Sea, this 

 byssus is so fine and silky that the Ital- 

 ians weave it with silk and make caps, 

 gloves and other articles of wearing ap- 

 parel. 



Another wonderful and interesting ar- 

 rangement for the comfort of the animal 

 is its breathing organs or branchiae. 

 These are two or four in number, and are 

 made up of numerous small chambers, 

 covered with little whip-like organs or 



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