BIVALVE MOLLUSC A. 317 



parisons. " The shell which serves as a dwelling and a shelter 

 •cannot," say these authors, " be considered as a skeleton, because 

 it does not assume the external form of the animal ; because it does 

 not attach itself to the organs of locomotion ; and, finally, because 

 it is the product of secretion, which increases in proportion to the 

 development of the body itself." The last two reasons appear to us 

 to be the most acceptable. 



However that may be, from the immense variety of form and 

 size, from the beauty and brilliancy of their colours, the shells of the 

 molluscs are among the most attractive objects of natural history. 

 Nor is it from their beauty alone that a fine collection of shells 

 becomes interesting : a living creature l^as inhabited the shell, a 

 creature which in its organisation and its life, above all, by its habits, 

 excites in a high degree our interest, curiosity, and admiration. It 

 has been said that the shell " is like a medal struck by the hand of 

 Nature to commemorate climates." In short, the waters of different 

 regions of the globe, whether fresh or salt, are characterised by the 

 presence of particular shells ; moreover, the comparison of living 

 shells with those which lie in a fossilised state buried in the deoths 

 of the soil is a most important element of our knowledge touching the 

 origin of the different beds out of which our globe is constituted. 



Thus, we must not shut our eyes to these beings, in appearance 

 so miserable and obscure, if we would possess a general knowledge 

 of the animal kingdom. The Creator has endowed them with many 

 wonderful gifts to embellish their lives, and who would dare to 

 disregard them ? Who could examine and compare their structure 

 without being charmed with the study ? Man, who descends into 

 the depths of the earth in search of the precious metals — who dives 

 into the deep in pursuit of the treasures it conceals — who stoops his 

 head over works of art — would surely not refuse to bend himself for 

 a moment to the sand of the sea, to gather in his hand, to bring 

 nearer to his eyes these marvellous works of the Divine Creator to 

 be found thereon ! 



ACEPHALA. 



We have seen that the Mollusca proper have been divided by 

 Cuvier into five sub-classes — the first of these is called Acephala. 



The Acephalous or Headless Molluscs are so called from the 

 Greek d, privative, and Ke(pa\yj, head. They have no head ; the body 

 is surrounded by the folds of the mantle ; the shell consists of two 

 valves. Such is a summary description of all the Acephalous 

 Molluscs. They are sometimes partially naked, but are for the most 



