COMPARATIVE ANATOMY. 



81 



COMPARATIVE ANATOMY. II. 



DIVISIONS OF THE ANIMAL KINGDOM VEBTIBRATA MOL- 

 A MOLLUHCOIDA ANNULO8A ANNULOIDA CUCLEN- 

 VTA PBOTOZOA. 



THK liiniii divisions of the animal kingdom, called sub-kingdoms 

 or branches, were first established on anything approaching 

 ntifio basis by the great Baron von Cuvier. Previous 

 'rs had endeavoured to mark out these divisions by 

 differences in some one organ or system of organs. The system 

 which was generally made use of, as producing the most natural 

 classification, was that of the organs of circulation of the blood, 

 or the nutritive fluid which answered to the blood. The classifi- 

 cation of animals according to the structure of their hearts, 

 blood-vessels, etc., was perhaps as good as any founded on any 

 one system of organs. At least, our groat anatomist, Hunter, 



*'u\i<-r ilividod the "nimal kingdom into four Bub-kingdoms, 

 M follow* : 



MoUtuca. 



Ariiculata. 



The three higher division* remain very much M he oonatitute'l 

 them. There could be no higher testimony to the value of these 

 than this, that all the multitude of higher .niml that have 

 been discovered or examined since his time fall naturally under 

 one or other of bis divisions. Cnvier himself amigned some 

 animals to the wrong branch, yet when the error was discovered 

 it did not necessitate the formation of a new syitem, bat merely 

 a transference from one branch to another ; and this proves cot* 

 clusively that the classification was not an artificial system 

 fitted on to his knowledge, which, though wide, was of course 

 limited, but was a recognition of the fundamental plan of 

 nature. 



I. SKETCH OF HADDOCK, SHOWING ITS EXTERNAL FORM, AND ALSO THE ARRANGEMENT or ITS INTERNAL ORGANS. II. TRANSVERSE SBCTIOV or 

 HADDOCK AS EXHIBITED AT THE LINE a b. III. SKETCH OF LOBSTER, SHOWING ITS EXTERNAL FORM AND THB AKRANGEXEKT or m 



INTERNAL ORGANS. IV. TRANSVERSE SECTION OF LOBSTER, EXHIBITBD AT THE LINE a 6. 



Ecfs. to Xos in Figs. I., II., III., IV. 1, heart; 2, nervous system ; 3, brain; 4. alimentary canal ; 5, vertebral column ; 6, sympathetic 

 nervous system. 



who had carefully examined all the systems of organs of animals 

 in relation to their use in classifying, thought so. It now, how- 

 ever, seems to be laid down as a rule that it will not do to rely 

 on any one character in classification. If a classification be 

 made in dependence on the modifications of but one organ, it is 

 euro to be an unnatural one. If, on the contrary, it can be 

 stated that any group of animals is distinguished from the rest 

 by peculiarities in two or more systems of organs, that group is 

 sure to be a natural one. Cuvier was more successful than his 

 predecessors, not so much because he had any better key by 

 which to interpret the animal kingdom, as because he relied on 

 no key, but trusting to his wide knowledge of the structure of 

 animals, and to his sagacious perception of what similitudes or 

 differences were fundamental and what were unimportant, he 

 made a classification which recognised the plan of structure of 

 each animal as a whole, that is, as made np of the sum of its 

 organs. The difficulties attending such a method are far greater, 

 the definitions of the branches thus formed are less simple and 

 precise, than those of the former methods, but the results 

 have the merit of being true to nature, and therefore stable. 



32 N.E. 



The lowest of those branches, designated Jladiatu, has not 

 maintained its ground as the others have, for the following 

 reasons. Many of the animals assigned to this branch are 

 microscopic, and had been but little examined, and Cuvier 

 founded his branch on the plan of structure exhibited by so ire 

 of the more conspicuous animals, such as the star-fish, and h 

 assumed that all the lower animals conformed to that plan of 

 structure. This, however, has been found not to be the fact. 

 Nor was the definition of this branch good as far as it went, 

 since it was founded on one peculiarity alone, namely, the plan 

 of structure. In fact, however derogatory the admission may 

 be to the great anatomist, we are compelled to admit that his 

 sub-kingdom Radiata stands in the same relation to the rest of 

 his admirable system, as the untidy lumber-room which gene- 

 rally exists in even a well-ordered house, and into which every- 

 thing which has no definite place of its own is thrown does to 

 the rest of the establishment. Most of us who make natural 

 history collections of any kind have in our cabinets a spare 

 drawer, into which specimens wo have not had time to examine 

 or to name, or whose place in the collection we are doabtf aj 



