312 THE BEAKED SPINDLE-SHELL. 
CER? AA LO HO RFA. 
WE now take leave of these highly developed mollusks, and pass to other forms where 
the organization is not nearly so perfect, and where the habits are either so commonplace as to 
be devoid of general interest, or the animals so shy that they never can be seen performing any 
act which is likely to attract the attention of an unprofessed naturalist. 
It is an enormously large group, containing all the snails, whether terrestrial, aquatic, or 
marine, the whelks, limpets, and similar animals not so familiarly known. Many species are 
much used as food, while others are of great service in the arts, furnishing employment to 
many hundreds of workmen. As the shell of these creatures consists of one piece or valve only 
they are sometimes termed univalves, in contradistinction to the oysters,muscles, scallops, 2nd 
similar shells, which are termed bivalves, in allusion to their double shell. 
The larger number of mollusks are divided between the class which embraces the bivalve 
shells and the present, the Cephalophora, or head-bearers ; the former are collectively termed 
Acephala, or headless. The present class naturally take rank next after the Cephalopods, 
so-called because the feet are arranged around the head, and both rank higher than the Ace- 
phala, the headess, for the reason that they are more like the higher forms of life; that is, 
they are symmetrical ; have heads with a pair of eyes. 
The term Gasteropods has heretofore been used to designate this order, from the fact that 
they crawl upon a flat disc, which was likened to a stomach, hence stomach-footed. 
The animals embraced in this order have what is called a lingual ribbon, or tongue, which 
consists of a band of chitine, a peculiar substance which is characteristic of the skins of insects. 
This is called an Odontophore, or tooth-bearer. It is attached to the floor of the mouth, and 
lies free at one end, and bears on its upper surface numbers of hard, tooth-like processes. 
When in use it is moved by muscles, and drawn over cartilages; a rasping motion brings the 
hard teeth into contact with any substance taken into the mouth for food. 
The mouth of these animals is situated on the under side of the head, and is armed by 
variously situated jaws or plates of the hard glutinous character. Classification has been 
greatly aided by the examination of these lingual ribbons. The symmetry of the typical 
Cephalophoras is lost in the largest number by conforming to the shapes of the external parts 
—their shells. The cavity of the mouth communicates with an zesophagus, which sometimes 
dilates and forms a crop, and then the stomach follows, from which the intestine arises. 
The circulatory system is well developed ; Dentalium being an exception, having no heart. 
One auricle and one ventricle is usually present. The blood is colorless, the corpuscles of 
which is nucleated. In both Acephala and the present class, the heart receives the blood from 
the gills and forces it over the body. 
Respiration is by gills or by pulmonary organs, lamellar in form, and by plume-like 
branchie. The nervous system differs in the various groups; ganglia or knots of nervous 
matter arranged about the anterior parts—around the ‘‘swallow,”’ for example—serve the func- 
tions of brain. Organs of hearing are present; eyes are generally so, and usually two in 
number, situated upon the head, or some projecting appendages, called tentacles. The eyes 
are singularly like those of vertebrates. The sexes are separate in some and in others com- 
bined in one individual. Most of these forms lay eggs. In a few the young are produced 
living, the eggs being hatched within the parent. 
Classification of these forms is yet in a most unsettled condition; further study is required 
for the determination of points of importance. Consequently provisional arrangement is all 
that the student can look for. This should, of course, be understood, as learners are apt to 
receive the mischievous idea that classification is fixed. 
Our first example of the gasteropods is the BEAKED SPINDLE-SHELL, so called from the 
rather distant resemblance which its long and pointed form bears to a spindle, and the 
elongated beak-like process which is seen pointing downwards to the ground as the animal 
walks along. In the family to which this mollusk belongs, the lip of the shell is always 
extended and deeply notched. 
