( 52 ) 
MOLLUSCA. 
CLASSES. 
A. With unwalve shells, or none. 
4. CEPHALOPODA. 
Body in the form of a A head covered with Sexes separate. 
bag, open before, con- large, long, fleshy pro- 
taining the branchiz. ductions, serving for lo- 
comotion and prehen- 
sion. ‘ 
2. PreRopoDa. 
Body entirely closed. Appendages of the Hermaphrodite. 
head small or none; or- 
gans of movement two 
Wings or membranous 
fins on the side of the 
neck, and frequently 
bearing the branchial 
tissue. 
3. GASTEROPODA. 
Creep on the fleshy disk A head distinct and Hermaphrodite and 
of the belly, sometimes anterior, or none. sexes separate. 
compressed into a fin (2). 
(1) These are the only Mollusca in which organs of hearing have been disco- 
vered, and which have the brain (sending forth innumerable optic nerves from the 
two ganglions) within a cartilaginous box: they are called Cephalopoda because 
they have the feet on the head. They have three hearts; they respire in water by 
branchiz ; their mouth is placed in the centre of their feet, and resembles a beak; 
the head is also distinguished by very large eyes, and has the ears placed inter- 
nally; the stomach is muscular like a gizzard, the liver very voluminous. A par- 
ticular gland secretes a black liquor, which they throw out, and which darkens the 
water around them whenever they wish to conceal themselves. They swim with 
their head behind; and walk in all directions with the head below and the body 
above. Aristotle remarked, that certain herbs, which have a strong odour, were 
avoided by cuttle-fishes and the octopus. 
(2) They are so called because they crawl on their bellies; the head is move- 
able, and frequently provided with tentacula ; the heart is single. 
When the name of the genus appears in the following tables without any cha- 
racteristic particulars, the animal is very imperfectly known, 
