302 THE MOLLUSKS. 
in those divisions. The lower forms ‘‘came tardy on.’’ Unfamiliar and plain folks, as it 
were, naturally less attractive ; though after a better acquaintance exhibiting many extremely 
interesting as well as beautiful members. The sea anemones are among the most exquisite of 
all Nature’s handiwork, both in color and structure, and the numberless microscopic forms 
now rapidly coming to light challenge our admiration and wonder, 

MOLLUSKS: 
Tue first group of invertebrated animals is called Motiusca. This term is yet retained 
for this great branch of the animal kingdom, almost meaningless though it be; for it simply 
expresses one, and a very unimportant, feature of this great group of animal life—that of 
softness. Probably some naturalist will stop in his work one day, and devote a little time 
to determining the best and most comprehensive term, one which will express the nature of 
the division asa whole. The term Arthropoda, as applied to the creatures formerly called 
crustaceans, because they had crusty-like shells, or coverings, seems to be much nearer a 
natural designation, as the creatures are all jointed or articulated. 
Mollusks are bilateral animals, that is, having two equal sides, though in some this is 
obscured by certain developments, as in the gasteropods. They are either provided with a 
bivalve or univalve shell, or none, as in the naked Mollusks. The shells are largely composed 
of carbonate of lime, with more or less animal matter, the whole being secreted by the inclos- 
ing mantle, from its outer layer. The shell is entirely without blood vessels. The internal 
soft parts have a central mouth and digestive tract terminating in an anus, which is primi- 
tively at the posterior end, and in the median line. The torsion produced by the growth in 
the spiral and other irregular shells obscures this, but careful study of the young makes this 
and many other seemingly difficult points clear. 
The nervous system is in the form of ganglia or knots of nerve matter with their connect- 
ing nerve lines. The cerebral ganglia, or brain, consists of two knots above the cesophagus, 
and pairs of knots are distributed around all the important viscera, as presiding centres of 
nerve power. The heart, situated near what is called the back (dorsally), consists of a ven- 
tricle and one or two auricles. It receives the blood from the respiratory organs, and forces it 
through the body. The whole surface of the body has respiratory functions, but special 
organs exist in the form of gills, or so-called lungs. As a rule, the sexes are united in the 
same individual, Numerous marine gasteropods have sexes distinct, and in all of the mem- 
bers of the highest order, the cephalopods, also. 
The power of progression in the Mollusks is greatly varied, being in some species almost 
absent, while in others it is developed to a wonderful degree. Many of these creatures, such 
as the mussel, the limpet, and the oyster, scarcely stir from the spot where they have once 
fixed their habitation ; the snail and those of a similar form glide slowly along by means of 
the curiously developed mass of muscular fibres, technically called, from its use, the foot ; the 
scallop drives itself through the water in short jerks or flights, caused by slowly opening and 
then rapidly shutting its valves; several species are known to jump by a sudden stroke with 
the foot; the nautilus urges its shell through the waves by the violent expulsion of water 
from its interior, and is driven along on just the same principle by which a sky-rocket soars 
into the air; and the flying squid, one of the cuttle-fishes, is able to rival even the fiying-fish 
in its aérial journeys, shooting through the air to considerable heights, and even leaping fairly 
over both bulwarks of a ship and alighting in the water on the opposite side of the vessel. 
The old fable of the nautilus and its sails has long been rejected, but the fabricators of 
this legend need not have visited the ocean for an example of a molluskan boat. Any one 
who is in the habit of watching the streamlets that irrigate while they drain our meadow 
