BIVALVE MOLLUSCA. 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 has 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 depths 
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 4, privative, and xepaa}, 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 
