ZOOLOGY. 



system from the general body cavity. In a typi- 

 cal vertebrate, such as man, it consists of a series 

 of bones or -vertebras, which are articulated to- 

 gether in such a manner as to permit of a greater 

 or less degree of flexibility, and giving attach- 

 ment to appendages, of which some support and 

 protect important viscera, while others assist in 

 the motion of the animal. Each vertebra has 

 more or less the form of a ring, and when the 

 various vertebrae are articulated together, the 

 whole is termed the vertebral column, or back- 

 bone. The ring-like apertures in each vertebrae, 

 when thus joined together, form a tube, in which 

 the spinal cord is lodged, and from which the 

 nerves which supply the body are given off. The 

 vertebral column is placed dorsally, and serves 

 not only as a surface of attachment for muscles, 

 and a central axis, but also as a protection for 

 the main masses of the nervous system, which 

 are thus also placed dorsally, and are separated 

 by a partition from the general body cavity. The 

 anterior extremity of the spinal column is expanded 

 in a box or case, the skull (technically called the 

 cranium), in which the brain is lodged. The 

 brain is continuous with the spinal cord through 

 an opening in the base of the skull, called the 

 foramen magnum. The theory that the skull is 

 composed of a series of vertebras, whose arches 

 are expanded, and unite to inclose and protect the 

 brain, originated with Goethe, in 1791, on his 

 picking up an old and broken sheep's skull amidst 

 the sandy dunes of the Jewish cemetery in Venice. 

 Lorenz Oken came independently to the same 

 conclusion, and in 1807 published his vertebral 

 theory of the skull. According to Professor Owen, 

 the skull is a continuation of the back-bone, and 

 consists of four vertebras or segments, correspond- 

 ing to the four consecutive enlargements of the 

 nervous system which we call the brain. These 

 segments, reckoning them from behind forwards, 

 are termed the occipital, the parietal, the frontal, 

 and the nasal segment. In the embryo of all 

 vertebrates, a structure called the notochord(notos, 

 back, and chorde, string), or chorda dorsalis, is 

 invariably present. It generally disappears in the 

 adult, but it is persistent in some fishes. It is a 

 cellular, rod-like structure, situated immediately 

 under the spinal cord, and out of which the 

 vertebral column and some other structures are 

 developed. The general bony fabric of which the 

 vertebral column is the main or central part, is 

 internal, an arrangement contrary to that in the 

 lower provinces of creation, where the hard and 

 sustaining parts are external. The limbs never 

 exceed four in number, and are turned ventrally, 

 serving for progression, and occasionally for pre- 

 hension or seizing, but subject to many variations, 

 according to the element in which the animal 

 lives, and the nature of its necessities. By reason 

 of their superior nervous system, vertebrated 

 animals stand decidedly above other provinces 

 in intelligence. With the single exception of the 

 Lancelet, all the vertebrata have red blood, which 

 is due to presence in the blood of an innumerable 

 multitude of minute red, round or oval bodies, 

 called blood-corpuscles, about -5-^ of an inch in 

 diameter, the fluid in which they float being itself 

 colourless. 



This sub-kingdom is divided into the five great 

 classes Fishes (Pisces), Amphibians (Amphibia), 

 Reptiles (Reptilia), Birds (Aves), and Mammals 



(Mammalia). By Professor Huxley, the fishes 

 and amphibia are grouped together under one 

 section, and called" Ichthyopsida, because at some 

 period or other they breathe by gills. The reptiles 

 and birds he puts into another section, under the 

 name Sauropsida, characterised by their never 

 possessing gills, by the skull being articulated to- 

 the vertebral column by a single occipital con- 

 dyle, by the articulation of the lower jaw to the 

 skull through the intervention of a distinct bone 

 (the os quadratum), and by the ramus of the 

 lower jaw being composed of several pieces. He 

 retains the name Mammalia for the mammals, 

 for the characters of which see Mammalia. 



CLASS I. FISHES. 



In this class, the animals are wholly aquatic, 

 and breathe by means of gills or branchiae. The 

 heart consists of a single auricle and ventricle. 

 The auricle receives the blood from the system, 

 and propels it into the ventricle, by which it is 

 sent on to the gills, where it is aerated by being 

 exposed to the air contained in the water, and is 

 then distributed throughout the body. The blood 

 is cold that is, it never rises in temperature above 



Fish: 



a, dorsal fins ; 6, pectoral fin of one side ; c, ventral fins ; d, anal- 

 fin ; e, caudal fin, or tail ; f t operculum. 



the temperature of the surrounding medium. The 

 four limbs of a typical vertebrate assume in fishes 

 the form of fins, and are generally, although not 

 always, all present, the first pair being the pectoral, 

 the second pair the ventral fins. When the 

 ventrals are placed far forwards, underneath or 

 in front of the pectorals, they are called jugular 

 fins. There are other fins, however, which are 

 not placed in pairs, towards the sides, but verti- 

 cally in the middle line ; one or more (dorsal) on 

 the back ; one or more (anal) on the ventral 

 aspect, behind the anus ; and one (caudal} at 

 the extremity of the tail. These last are called 

 the unpaired fins, in contradistinction to the 

 former or paired fins. The chief propelling power 

 resides in the vertically flattened caudal fin or 

 tail, which is used by the fish in the same way as 

 a single oar is employed in sculling along a boat. 

 The pectoral and ventral fins serve chiefly for 

 balancing the body, while the dorsals and anals, 

 like the keel of a ship, keep it in its proper position. 

 The surface of the body is usually covered with 

 scales. In many species, the gills are covered by 

 a corneous plate, styled the operculum. In those 

 fishes which have a well-formed vertebral column, 

 the individual vertebrae are hollowed on each side, 

 with a bag of lubricating fluid between them, an 

 arrangement which gives great suppleness and 

 agility of movement They are nearly all ovipar- 

 ous, and some are amazingly productive. The- 



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