ICHTHYOLOGY 



LESSON V. 



CLASS OF FISHES. Genera/ Characters. Form. Integuments. 

 Skeleton. Muscular Apparatus. Swimming- Bladder. 

 Senses. Apparatus of Diyestion. Circulation. Itespira- 

 tion. JJniwcil Electricity. Habits Fishiuy Classification. 



CLASS OF FISHES. 



The fourth, and last Class of the Branch of Vertebrate Ani- 

 mals, comprises the Fishes : that part of Natural History which 

 treats of them, is termed Ichthyology, from the Greek, iclitkus, a 

 fish, and luyos, a discourse. 



1. These animals, as every body knows, are destined to live 

 under water, and this circumstance has impressed upon them a 

 peculiar organization ; but the most important differences they 

 present, when compared with other vertebrata, consist in the 

 conformation of the apparatuses of respiration and circulation. 

 They never have lungs, and always breathe by branchiae only. 

 Their heart has but two cavities, and only receives venous 

 blood, which, after being in contact with oxygen, enters a dorsal 

 vessel, where no new motive force accelerates its course to 

 different parts of the body. Therefore, their circulation is not 

 as active as it is in the superior animals, and like that of reptiles, 

 their blood is cold. Their skin is naked, or covered with scales 

 only ; they have no mamma3 like the mammalia, and are repro- 

 duced by the means of eggs ; their extremities are in the form of 

 fins. 



2. The external form of fishes varies; but their body is gene- 

 rally all of a piece. The head, which is of the same size of the 

 trunk, is not separated from it by a narrowing like the neck of 

 the superior vertebrate animals, and the tail, owing to its size at 

 the base, is not distinguishable from the rest of the body. Some 

 of these animals are entirely without fins ; but in most of them 

 we find a considerable number of these organs, some placed on 

 the middle line of the back or belly, and consequently unpaired 

 or singly, and others on the side, arranged in pairs. The latter 



1. What are the general characters of Fishes? What is the peculiarity 

 f their respiration '! How does their heart differ from th.it of mammals 7 



2. What is the greneral form of Fishes ? What is the situation of the 

 pectoral fins ? Where are the ventral fins placed ? What are dorsal fins 7 

 What is the situation of the anal fin ? What are the caudal fins? 



