Introduction. xvii 
4. Acephala, or Headless Mollusca. These animals have no apparent 
head, and breathe by means of branchiae, which are generally 
ribbon-shaped. Most of them are enclosed in a bivalve shell, 
but some are naked ; the former are the Testacea of Cuvier, and 
the Conchifera of Lamarck ; the latter are the Tunicata of 
Lamarck. They form two orders. 
5. Brachiopoda, or Arm-footed Mollusca. These animals also have a 
bivalve shell ; but they have no true branchiae, and their respi- 
ration is effected by the agency of the mantle. They have two 
spiral arms. 
6. Clrrhopoda, or Curled-footed Mollusca. These are generally attached, 
and enclosed in a shell of several pieces ; they are furnished 
with a mouth, armed with jaws, and with several pairs of jointed 
and fringed organs, called cirri, by the protrusion and retraction 
of which they capture their prey. Examples of this class are 
the Barnacles and Acorn shells. These animals have long 
ceased to be regarded as Mollusca, the investigations of modem 
naturalists having proved them to be true articulated animals 
most nearly related to the Crustacea. 
THE AKTICULATED ANIMALS 
Have no back-bone. The covering of the body is sometimes hard and 
sometimes soft, but it is always divided into segments by a number of 
transverse incisions. The limbs, when the body is provided with any, 
are jointed; and they can be separated from the body without any 
serious injury being sustained by the animal, new limbs being shortly 
after formed to replace them. The senses of tasting and seeing are 
more perfect than those of the Mollusca, though that of feeling seems 
much less acute. In other respects the four classes differ considerably 
from each other. 
[ The Entozoa, or Intestinal Worms, placed by Cuvier and others 
among the Radiata, are now arranged amongst the lowest forms of 
articulated animals, as are also those animalcules known as Eotifera.'] 
The Annelida, or Red-blooded Worms, have no heart, properly so 
called, but have sometimes one or more fleshy ventricles. They 
breathe through branchiae. Their bodies are soft, and more or 
less elongated, being divided into numerous rings or segments. 
The head, which is at one extremity of the body, can scarcely 
be distinguished from the tail, except by having a mouth. These 
animals have no feet, properly so called, but they are furnished 
with little fleshy projections, bearing tufts of hairs or bristles, 
which enable them to move. They are generally of carnivorous 
habits. They lay eggs, but the young are frequently hatched 
before exclusion, and hence these creatures are said to be ovo- 
viviparous. Their study is called Helminthology. As examples 
of the three orders of this class may be mentioned the serpulae 
or worm-like animals, often found on shells, the common earth- 
worm, and the leech family. 
The Crustacea comprise the shell-fish commonly called crabs, 
lobsters, shrimps, and prawns. They have a distinct head, fur- 
nished with antennae, eyes, and mouth : and their bodies are 
C 
