Introduction. 



OKDEKS OF FISHES. 



Fishes constituted Linnseus'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 ventral 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 Linnaeus 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. 



