ICHTHYOLOGY. 



205 



Introduc- nius of their time, they continued to attacli miidi more 

 tion. importance to the ascertainment of tlie names which 



^*^~v^^ tlie species bore in the classical pages of antiquity, than 

 to the composition of their history, as it were afi-esh, by 

 the light of nature and their own knowledge. Never- 

 theless, they rectified as well as extended the observations 

 of Aristotle, and laid a positive foundation of the subject, 

 by figures and descriptions of a cerUiin number of well- 

 determined species. About the close of the seventeenth 

 century, Willughby, and his illustrious friend John Hay, 

 gave for the first time a history of fishes, in which the 

 species were not only clearly described tioni nature, but 

 distributed in accordance with characters drawn solely fi-om 

 tlieir structure, and in which we are no longer unneces- 

 sarily burdened with inapplicable passages from either 

 Greek or Roman writers. Finally, about the middle of 

 the eighteenth century, Artedi and Linnanis completed 

 what the others had commenced, by establishing well- 

 defined generic groups, consisting of ascertained species 

 precisely characterized. From that period it may be said 

 that no radical defect existed, nor any olistacle in the way 

 of a gradual perfecting of the system, which could not be 

 overcome by zeal, accuracy, and perseverance. Never- 

 theless, it is to the genius of Baron Cuvier that we owe 

 the gigantic stride which has been made in our own more 

 immediate days. 



It is only by a profound study of the whole animal struc- 

 ture that we can, to the extent of our limited intellect, 

 correctly appreciate that part of the works of the great 

 Creator, and get some insight into the branching and anas- 

 tomosing affinities by which the almost numberless kinds of 

 living beings are linked together. Many years spent in 

 anatomical investigations gave Baron Cuvier such a know- 

 ledge of the mutual dependence of the various parts of the 

 organism of each of the numerous species which came 

 under his observation, that he v/as able, from the inspection 

 of a single bone, to reconstruct, mentally as it were, the 

 animal to which it had belonged, and to assign the species 

 its place in the system of nature. This great step in the 

 history of Zoology placed its discoverer in the first rank of 

 the cultivators of the science. In none of the greater di- 

 visions of the animal kingdom were Cuvier's labours, in 

 forming a natural arrangement of the species, of more value 

 than in the class of Fishes, the lowest of the vertebrata, 

 or of that division of animals whose proper character 

 consists in the possession of a central bony axis on which 

 the soft parts are sustained, and from which the motive 

 powers diverge. The Latin word used above has been adopt- 

 ed into the English scientific language, though by many 

 the more Anglicised term of " vertebrals" is used, and vie 

 call the internal chain of bone the vertebral column, while its 

 several successive component joints are named " vertebrae." 

 The German equivalent of vertebrata is " wirbelthiere." 



We must remark, at the outset, that neither this term of 

 Vertebrata, nor any other definition of a group which the 

 ingenuity of man has hitherto devised, is logically correct. 

 In Mammals, indeed, the highest class of the division, 

 the internal bony frame is strong and massive, and fitted to 

 support the limbs, by which, with the firm earth for a ful- 

 crum, the animal moves through a medium greatly lighter 

 than itself. In Birds, too, constituting the second class of 

 the division, the bones of denser texture but more slender 

 form and often hollow, are admirably fitted for sustaining 

 the powerful muscles exercised in the maintenance of ex- 

 tended aerial flight ; and in both classes, the turning joints 

 of the vertebral cohimn, and more especially of the cervical 

 portion of it, are adapted to the various motions of the ani- 



mal, and for enabling it to rotate its head from side to side, 

 and survey whatever comes within its field of vision. As 

 we descend to the less highly organized vertebrals, we come 

 to other and remarkable modifications of the spinal column. 

 In the third class, or the Ileptiles, there is one order, 

 namely, that of the Ophidia, or Serpents, whose locomotion 

 is perfiirmed by creeping without external limbs, and solely 

 by the flexibility of the vertebral column and the muscles 

 attached to it, and to its appendages the ribs. The verte- 

 brae are accordingly much more numerous in these animals 

 than in any others, and their motions on each other more 

 extensive. In another group of the same class the vertebrae 

 of the body are soldered together by bone, and power of 

 motion is preserved only in the neck and short tail. A 

 third group, named Amphibians, are fishes in their embryo 

 or tadpole condition, and undergo a kind of metamorphosis 

 in becoming terrestrial and air-breathing creatures. A 

 fourth remarkable group, of which only a few sjiecies have 

 been hitherto detected, presents, with much of the piscine 

 form, the peculiarity of the existence of both gills and lungs, 

 and a residence in water during life. In the Fishes, the 

 proper subjects of this treatise, and the lowest class of ver- 

 tebrated animals, there is a large group named by some 

 authors Caktilaginei, or Cpiondkopterygii, because the 

 internal skeleton remains in the state of cartilage, the bony 

 structure being wholly absent in some species, and in others 

 only very partially present ; and thus the precision of one 

 part of the character of the vertebrata given above is im- 

 paired. In certain of the Cartilaginei the joints of the 

 column are obsolete, and flexibility is substituted for the 

 turning motions indicated by the word vertebrie. These 

 brief notices point at some of the difficidties which beset 

 the zoologist when he endeavours to convey the knowledge 

 he has acquired to others, by concise and definite phrases. 

 Yet however difficult it may be to construct a correct de- 

 finition, it is certain that the idea of the type of an animal 

 group may be conceived in the mind, on the basis of exact 

 observation and legitimate deduction, in proof whereof the 

 reader is confidently referred to the works of Professor 

 Richard Owen of the British Museum, antl particularly to 

 his treatise On the Archeti/pe and Homologies of the Ver- 

 tebrate Skeleton} 



The vertebrated animals agree in having a spinal chord 

 or elongated bundle of nervous filaments running along the 

 body, and protected by bony arches composed of the neural 

 apophyses, or processes which rise upwards from the body 

 or centrum of each vertebra. The anterior expansion of 

 the spinal chord, named the brain, is most fully developed 

 in the higher classes of vertebrals, and is comparatively 

 very small in fishes whose encephalon has the character of 

 a series of ganglions, or knots of nervous matter, arranged 

 in single succession or in pairs. In the lowest known form 

 of fish, the Lancelet, the whole vertebral column is merely 

 a pulpy nervous chord invested by a membranous sheath ; 

 and Pallas, the first describer of this animal, ranked it, in 

 accordance with the progress that science had made in his 

 time, among the Slugs. In all the vertebrals the vascular 

 trunks and organs of digestion are protected by the inferior 

 processes and diverging appendages of the vertebrae ; and 

 the type of this division of animated beings is essentially 

 tetrapodal (fig. 1 ), though in some groups one or both pairs 

 of limbs are either rudimental or absolutely wanting — ex- 

 amples of these deviations tiom the oi'dinary type being 

 most frequent in the classes of Reptiles and Fishes. The 

 four limbs are produced in lateral pairs ; and in fishes the 

 first pair are named pectoral fins, and the second pair, being 

 situated on the ventral aspect of the fish, are called ventral 



Introduc- 

 tion. 



^ On the Archetype and Homoloyies of the Vertebrate Skeleton, 8vo. London, 1849. Also Report of the Britisit Association, 184G — Oft {A» 

 nature of Limbs ; lUchard Owen, &c., 8vo. London, 18i9. 



