viii INTRODUCTION. 



as they support that column ; and their forms and relative developments, like those of all 

 the other parts, depend on the habits of the animal. 



The muscles, or organs of motion, in those animals, are, with the exception of some that 

 answer particular purposes in the economy, and are mos^j styled involuntary, inserted in 

 the bones, one on each side of a joint, and they pull the diMal bone, or bone farthest from 

 the spine, into a new position by their contraction. 



The skin, or external covering, is flexible, and consists of an epidermis or cuticle, a 

 mucous tissue, and a corium or true skin. The appendages to it are fur, hair, feathers, or 

 scales ; and while the animal is in health it is capable of resisting both air and water at the 

 ordinary temperatures. 



The brain, or cerebral mass, with its continuation in the spinal column, and the pro- 

 longation in various nerves or chords, forms the system of sensation. The other systems are 

 the nourishing, the circulating, the respiratory, and the productive. 



The nourishing system consists of the mouth, the stomach, and the intestinal canal, by 

 which the food is received and assimilated so as to render it fit for being mixed with the 

 blood. 



The circulating system consists of a heart, arteries, and veins. The heart, even for 

 one system, consists of two cavities, a ventricle, or more muscular one, which propels the 

 blood through the arteries, and an auricle, or weaker one, which receives it on its return 

 through the veins. But in most animals of this division there are two systems, one of them 

 pulmonic, or receiving the blood from the body, and sending it to the lungs or other organi- 

 sation that answers a similar purpose and the other systematic, receiving the blood from 

 the lungs, and circulating it over the body. By the systematic arteries the waste of the 

 body is supplied ; and by the returning blood through the systematic veins, the matter which 

 has ceased to be fit for the purposes of life is taken up. The blood, thus loaded with the 

 waste of the system, is sent to the lungs, or other respiratory organs, where the refuse, which 

 appears to consist principally of charcoal, unites with the oxygen of the air, in the case or 

 lungs, or with oxygen separated from water in the case of gills ; and these combined are 

 given out in the state of carbonic acid gas, and in very nearly the same volume as the oxygen 

 required. 



The respiratory system is for the supply of the oxygen, to accomplish which air is 

 taken into the cells of the lungs, or water made to pass between the fibres of the gills, 

 the blood being in the mean time exposed to it, not naked, but in minute vessels, of which 

 the coats are exceeding delicate. The details of these systems, further than they are 

 connected with the external appearances and characters of animals, belong to physiology 

 rather than to this branch of the science. 



In the productive system the males and females are, in most instances, different 

 individuals, and they are viviparous, oviparous, or ovoviviparous. The first, which bring 

 forth their young alive, are either placenlal or marsupial, the former bringing forward their 

 young in an internal uterus ; the latter bringing them forward in a marsupium, or pouch on 

 the abdomen, which also serves as a bag for carrying them in while they are very young. 

 The oviparous produce eggs, which are hatched externally, with or without the heat of the 

 parent, according to the species ; and the ovoviviparous produce eggs which are hatched 

 internally, and the young brought forth alive. The last of these bear some slight resem- 

 blance to the marsupial animals ; and it is said that the young, in the very early state> 

 sometimes take refuge in the envelope in which they were hatched ; but this fact is not very 

 clearly ascertained. 



In all cases, however, the young is, from the very beginning, that is, from the first 

 rudrmental state in which it can be traced, a being distinct and separate from the mothe* ; 



