FOUR GRAND DIVISIONS OF THE ANIMAL KINGDOM. 



21 



petrifaction must also, in some instances, have commenced almost 

 immediately after the death of the animal. In some specimens of 

 fossil fish from chalk, in the museum of Mr. Mantel! of Lewes, the 

 air-bladder is uncompressed, and filled with mineral matter. 



In tracing the different animal remairiS that occur in the lower, the 

 middle, and the upper strata, the circumstance most worthy of notice, 

 is the first appearance of any of the different divisions and classes 

 of animals, and of the orders, genera, or species belonging to each 

 division. In the luminous arrangement of Baron Cuvier, in his 

 Regne Animal, all animals are distributed, according io their organ- 

 ization, into four grand divisions — Vertehrated, Molluscous, Articu- 

 lated, and Radiated. 



1st, Vertehrated. — Animals which have a skull, containing the 

 brain, and a spine or back bone, containing the principal trunk of the 

 nervous system, commonly called the spinal marrow : they have red 

 blood. This division comprises the mammalia (or animals that suckle 

 their young), birds, reptiles, and fishes. 



2d, Molluscous. — Animals in this division have no internal skele- 

 ton : the muscles are attached to the skin, which, in many species, is 

 covered with a shell. The nervous system and viscera are compo- 

 sed of detached masses, united by nervous filaments : they possess 

 only the senses of feeling, taste, and sight; but many species want 

 the latter. They have a complete system of circulation, and partic- 

 ular organs for respiration. Animals with bivalve, univalve, or with 

 chambered shells, belong to this division ; but many molluscous 

 animals have no shell. 



3d, Articulated. — To this division belong worms, crustaceous an- 

 imals, and insects : their nervous system consists of two long chords, 

 ranging along the body, and swelling out in different parts into gang- 

 lions and knots. Worms having their bodies composed of rings, are 

 called annelides; they have red blood: some species inhabit a cal- 

 careous tube, supposed to be formed by exudation. 



4th, Radiated — comprises all the animals which were by former 

 naturalists called zoophytes, or animal plants, as the corallines, he. 

 which were long mistaken for marine vegetables. In animals of this 

 division, the organs of sense and motion are disposed circularly 

 around a centre or axis. They have no distinctly marked nervous 

 system, and the traces of circulation in many species can scarcely be 

 discerned. Many of the animals in this division have no power of 

 locomotion, as madrepores and encrinites. Others, as the echinus, 

 possess a very complex organization, and the power of moving from 

 place to place on their spines, which serve them for feet. 



In describing the order in which the organic remains belonging 

 to each of these grand divisions are distributed through the different 

 classes of rocks, it will be more convenient to begin with the lowest. 



Radiated Animals, such as encrini and madrepores, have left their 

 remains dispersed abundantly through rocks of the transition series : 



