Introduction. 
ORDERS OF FISHES. 
Fishes constituted Linnaeus's fourth class of animals. They are all 
inhabitants of the water, in which they move by certain organs called 
fins. Those situated on the back are called dorsal fins ; those on the 
sides, behind the gills, pectoral fins ; those below the body, near the 
head, are ventral ; those behind the vent are anal ; and that which 
forms the tail is called the caudal fin. Fishes breathe by gills, which, 
in most species, are situated at the sides of the head. Fishes rise and 
sink in the water, generally by a kind of bladder in the interior of the 
body, called an air-bladder. Some of them do not possess this organ, 
and consequently are seldom found but at the bottom of the sea, from 
which they can only rise by an effort. The bodies of these animals 
are usually covered with scales, which keep them from injury by the 
contact of the water. 
The fishes were divided by Linnaeus into four Orders : 
I. Apodal.— Having no central fins, as the eel. 
II. Jugular.— Having the ventral fins situated in front of the pectoral 
fins, as the cod, haddock, and whiting. 
III. Thoracic. — Having the ventral fins situated directly under the 
pectoral fins, as the perch and mackerel. 
IV. Abdominal.— Having the ventral fins on the lower part of the 
body below the pectoral fins, as the salmon, herring, and carp. 
ORDERS OF INSECTS. 
The fifth class of Linnaeus comprised the Insects ; and the branch of 
Zoology which treats of them is calledEntomology. Nearly all insects 
go through certain great changes at different periods of their existence. 
From the egg is hatched the larva, which is a grub or caterpillar, and 
destitute of wings; this afterwards changes to a pupa, or chrysalis, 
wholly covered with a hard shell, or strong skin, from which the perfect 
or winged insect bursts forth. Spiders and their allies, which were 
included by Linnoeus in the insects, issue from the egg in nearly a 
perfect state. 
Linnaeus divided his class of insects into seven Orders : 
I. Coleopterous. — Having elytra, or crustaceous cases covering the 
wings ; and which, when closed, meet in a straight line along 
the middle of the back, as the cockchafer. 
II. Hemipterous.— Having four wings, the upper ones partly crusta- 
ceous, and partly membranous ; not divided straight down the 
middle of the back, but crossed, or incumbent on each other, as 
the cockroach. 
III. Lepidopterous.— Having four wings covered with fine scales 
almost like powder, as the butterflies and moths. 
IV. Neuropterous. — Having four membranous and semi-transparent 
wings, veined like network ; and the tail without a sting, as 
the dragon-fly and ephemera. 
