ANIMAL KINGDOM. 



107 



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(T. Bell.) 



ANIMAL KINGDOM, an appellation 

 given to that great division of natural bodies 

 to which ANIMALS belong. Like the other 

 kingdoms of nature, the mineral and the vege- 

 table, it is divided into numerous sub-king- 

 doms, classes, orders, genera, and other subor- 

 dinate groups, according to the properties and 

 forms of the objects which it comprehends. 

 As the primary grand divisions of the mineral 

 kingdom are founded on the primitive forms of 

 crystallization, and those of the vegetable king- 

 dom on the endogenous and exogenous modes 

 of growth, zoologists have endeavoured to find 

 some common principle for their first divisions 

 of the animal kingdom. The most common 

 function in animals, and in all organized beings, 

 is generation, and we find the animal kingdom 

 divided into four distinct groups by the modifi- 

 cations of this function, viz., fasipara, gemmi- 

 para, ovipara, and vivipara. But as the fissi- 

 parous and gemmiparous modes of generation 

 are effected without the presence of distinct 

 permanent organs, as the fissiparous mode 

 occurs in isolated species belonging to classes 

 remote from each other in the scale, and as 

 nearly all the classes of the animal kingdom 

 belong to the oviparous division, the modifica- 

 tions of this system do not present the means 

 of establishing primary divisions suitable for 

 the purposes of zoology. Although the pro- 

 cess of internal digestion is not so universal 

 as the Junction of generation, the internal 

 alimentary cavity is the most universal organ 

 of animals, and its forms therefore merit a 

 first consideration in the establishment of pri- 

 mary groups. It is found, however, that in 

 animals whose general structure is nearly the 

 same, the alimentary apparatus varies so much 

 according to the nature of the food, as to render 

 hopeless any attempt to subdivide the animal 

 kingdom from its modifications; as from its 

 having one or two apertures, from its being 

 a simple sac or a lengthened intestine, from 

 its having one, two, or more stomachs or glands 

 developed in its course, or other modifications 

 of this kind. 



In the circulating system we are presented 

 with better means for such divisions than in the 

 digestive, for the radiated classes have only 



vessels for their circulation, the articulated 

 classes have a superadded ventricle, the mollus- 

 cous classes and fishes a bilocular heart, am- 

 phibia and reptiles a trilocular heart, and the 

 birds and mammalia have four cavities in that 

 organ. The respiratory organs likewise afford 

 the means of founding primary divisions, as 

 into ciliated, branchiated, and pulmonated 

 classes, in ascending from the lowest to the 

 highest forms of that system. 



The primary divisions of the animal kingdom 

 adopted by Aristotle, viz., animals with red 

 blood and animals without red blood, are ob- 

 viously founded on a single principle of classi- 

 fication, and correspond with the more recent 

 divisions of vertebrata and invertebrata ; but 

 from the number of distinct classes of animals 

 now comprehended under each of these divisions, 

 they are quite unsuitable as primary groups in 

 the present advanced state of the science of 

 zoology. Considering the functions of the 

 nervous system or the intellectual conditions of 

 animals as a means of classification, Lamarck 

 proposed three great divisions, the lowest of 

 which comprehended the animals regarded by 

 him as apathic or automatic, the second the 

 sensitive, and the highest the intelligent, which, 

 however, are too hypothetical to answer the 

 purposes of the zoologist. Without any fixed 

 principle for the establishment of his primary 

 groups, Cuvier divided the animal kingdom 

 into the radiated, the articulated, the molluscous, 

 and the vertebrated divisions, which have been 

 generally adopted by naturalists. From the 

 importance of the nervous system in the living 

 economy of animals, some have sought in its 

 modifications a means of establishing primary 

 or grand divisions of the animal kingdom on 

 principles more uniform and philosophical than 

 those commonly employed. In the radiated or 

 lowest classes of animals, wherever the nervous 

 system is perceptible, as in actinia, medusa, 

 beroe, asterias, echinus, holothuria, &c. it is 

 found in the form of filaments disposed in a 

 circular manner around the oral extremity of 

 the body. This lowest form of the nervous 

 system is expressed by the term cyclo-neura, 

 and although, like the radiated and every other 

 character assigned to these classes, it is of 

 partial application, it marks the uniform con- 

 dition of that system on which the manifesta- 

 tions of life are chiefly dependent, and which 

 principally establishes the relations of animals 

 to surrounding nature. A different form of the 

 nervous system is found in the long cylindrical 

 trunks of the helminthoid and entomoid classes, 

 where we observe almost from the lowest ento- 

 zoa to the highest Crustacea, a double nervous 

 chord or column extending along the whole of 

 the ventral surface of the body. This form of 

 the nervous system, common to the articulated 

 classes of animals, is expressed by the term 

 diplo-neura, and it is found to accompany an 

 organization generally more complex than that 

 of the cyclo-neurose classes, and inferior to that 

 of most of the succeeding divisions or sub- 

 kingdoms, especially in the organs of vegetative 

 or organic life, as the vascular, the digestive, 

 and the glandular apparatus. The nervous 



