34 
THE LIVING WORLD. 
central surface. It is distinguished alike for longevity and for a singular 
tenacity of life. It is said that after many years’ enforced sojourn in the 
cases of a museum, the snail has been known to proceed as though there had 
been no interruption of his opportunities and no disuse of his services. Their eggs 
are produced in the necks of the snails, just as if even at this early period the 
PERIWINKLE AND GARDEN SNAILS- 
parent would gather her young to her bosom. As the snail grows it builds 
additional stories or whorls in its shell, and as it needs at each increase yet 
more commodious quarters, the front whorls are of greater size. 
The edible Heart Mussel (CarcLium eduele) prefers brackish water to 
salt, and hence is so plentiful about the Thames as to give rise to an almost 
separate industry. It is not so very palatable, but from its great numbers and 
the ease with which it is caught, it forms in English life what the Americans 
would call an “ institution.” 
If I were to describe conscientiously the several classes of creatures that 
furnish an unbroken chain—in which there would be many links—connecting 
the cephalopods with fishes, it would be necessary to 
pass over a very wide field, in which we would find not 
only vast numbers of animals, but many distinct orders 
as well. I would have to give space to a description of 
hundreds of mollusks, which are interesting because 
of the beautiful shells in which many of them have 
their houses, but tedious, at best, when it is attempted 
to portray them ; next to these would be the slugs and 
linnets, members of the same family, but without charm¬ 
ing shells to recommend them; and the gasteropods, or 
sea snails, that are as uninviting as our common garden 
species; and myriads of the Bryozoa , or u moss ani¬ 
mals,” which are so nearly vegetable that one may be 
grafted upon another, or one may be converted into 
several by separation, but which are interesting only to the microscopist. The 
coral workers, called Polyzoa , would next claim our attention, to pursue which 
would lead into many devious passages where we could hardly find our way 
without the light of a classical dictionary. And so, to prevent wearying the 
reader, and to avoid the charge of attempting the compilation of a work for 
the scientist rather than for the masses, I have resolved to confine myself, as 
stated in the introduction, to those forms of life with which we have more con¬ 
cern than mere idle curiosity, and thus provide a practical work for every day 
consultation, instead of a book suited only to those who have abundance of 
time for deep investigation and indulgence. 
HEART MUSSEL. 
