COMPARATIVE ANATOMY. 
5. Ammodites, launce. 
6. Ophiijliim. 
7. Stromateus. 
8. Trichiurus. 
II. Thoracici; ventral fins directly under 
the thoracic. 
1. Echeneis, .sucking fish. 
2. Coryphacna, dorado. 
3. Zeus, dory. 
4. Pleuronectes, flounder, plaice, 
dab, holibut, sole, turbot. 
.5. Chzetodon. 
6. Sparus. 
7. Perea, perch. 
8. Scomber, mackarel, bonito, tun- 
ny- 
9. Mulhis, mullet, &c. &c. 
III. Abdominales ; ventral fins behind 
the thoracic ; chiefly inhabit fresh water. 
1. Cobitis, loach. 
2. Silurus. 
3. Salmo, salmon, trout, smelt. 
4. Esox, pike. 
b. Clupea, herring, sprat, shad. 
6. Cyprinus, carp, tench, gold-fish, 
minow, &c. &c. 
IV. Jugulares; ventral fins in fi-ont of 
the thoracic. 
1. Gadiis, haddock, cod, whiting, 
ling. 
2. Uranoscopns, star-gazer. 
3. Blennius, blenny. 
4. Callionymns, dragonet. 
5. Trachinns, weaver. 
The animals which have no vertebral co- 
lumn, do not possess so many common cha- 
racters as the vertebral classes ; their hard 
parts, when they have any, are generally 
placed on the surface of the body ; the cen- 
tre of the nervous system, instead of being 
nclosed in a bony case, lies in the same ca- 
vity with the viscera; the cesophagus is 
generally surrounded by a nervous chord 
coming from the brain ; their respiration is 
not carried on by lungs, and they have no 
voice ; their jaws move in various direc- 
tions ; they have no urinary secretion. 
The invertebral animals were distributed 
by Linnasus into two classes ; insects and 
worms (vermes). The anatomical structure 
pf these animals was very imperfectly 
known, when the Swedish naturalist first 
promulgated his arrangement. But the la- 
bours of subsequent zoologists, and particu- 
larly those of Cuvier, have succeeded in es- 
tablishing such striking and important dif- 
ferences in their formation, that a subdivi- 
sion of the Linnman classes became indis- 
pensably necessary. The insects of Lin- 
naeus are divided into Crustacea and in- 
secta : and the vermes of the same author 
form three classes ; viz. Mollusca, Vermes, 
and Zoophyta. 
The Mollusca derive their name from 
the soft fleshy nature of their body. This 
class includes those pulpy animals, which 
may either be destitute of an external co- 
vering, when they are called mollusca nuda, 
as the slug ; or may be inclosed in one or 
more shells, as the snail, oyster, &c. when 
they are termed testacea. 
The animals of this class have no articu- 
lated members ; they have blood-vessels, 
and a true circulation; they respire by 
means of gills ; they have a distinct brain, 
giving origin to nerves ; and a spinal mar- 
row. 
1. Sepia, cuttlefish. 
2. Argonauta. 
3. Nautilus. 
4. Limax, slug. 
5. Aplysia. 
6. Doris. 
7. Clio. 
8. Patella, limpet. 
9. Helix, snail. 
10. Haliotis, Venus’s ear. 
11. Mtirex, caltrop, or rock.shelL 
12. Strombus, screw. 
13. Buccinum, whelk. 
14. Ascidia. 
15. Thalia. 
16. Ostrea, oyster. 
17. Soien, razorshell. 
18. Cardium, cockle. 
19. Mytilus, muscle, &c. &c. 
Cuvier classes the numerous genera of 
this order under the three following divi- 
sions: 1. Cephalopoda, (from xEf«x>i the 
head, and vtu; the foot) which have their or- 
gans of motion placed round the head; 
2. Gasteropoda, (from yaraf the belly, and 
ttb;), such as crawl on tlie belly; and 3. Ace- 
phala, (from a privative, and xefaXa), whicii 
have no head. The three first genera be- 
long to the first division; the ten succeed- 
ing ones come under the second ; and the 
remainder exemplify the last order. 
According as the shell of the testaceous 
mollusca consists of a single convoluted 
tube ; or of two or more separate pieces, 
they are called cochle® bivalves, multi- 
valves, &c. 
Crustacea possess a hard external cover- 
ing, and mimerous articulated members ; 
