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Show 30 lNTRODUCTION • . . dom into Four Great Gene?·al disb·ibution of the ~n_zr~wl J{zng Dzvzswns. . . 1 of the preJ.U d'I C es founded o. n t.h e If divestmg ourse ves 'd ly the orgamzatiOn ' d . d we consi er on .. divisions formerly a mitte.' e ard to their size, ubhty, and nature of animals, Without rhg f them and other ac- 1 k ledge we ave o ' . . the greater or ess now 1 fi d there are four prmCipal cessary circumstances, we shal nb o expressed, on which 1 1 ·r 't may e s . forms, four genera pans, I I d 11 d and whose ulteriOr all animals seem to h ave be.e n mo e e ' 1 "th which naturalists have divisions, whateve~ be thel ti\~; ~: modifications, founded on decorated them, ate mere Y g t . parts which produce the development or ad dI. ti·O n of. cer am ' no essential change in the plan I~~e~. is that of man, and of the In the first of these forms, w I? h b · and principal bl' him t e ram animals most nearly resem mg 1' d I·n a bony envelope, trunk of the nervous sY stem are enc ose th ·des of this in-formed by the cranium and ve~te~·re; ·~~ a~:l bones of the termedial column are attache t ke :\h~ body. the muscles limb~ which form the frame wor o ' . while "'' h otions they occaswn, generally cover the ~ones, ~ ~se ~ head and trunk. Anithe viscera are contamed within t e mals of this form we shall denominate .flnimalia Ve;tebrata. They have all, red blood, a museu 1a r h ear t ' a mouth furh· . bed with t'w o J.a ws S.i tuate d m· t h ei . ab ov e or before eac d :~~er, distinct organs of sight, hearing, smell and ta;~e t·:~, in the cavities of the face, never more tha~ fo.ur .Im sf the sexes always separated, and a very similar distributiOn o medullary masses and the principal branches of the nervous system. f th' great By a closer examination of each of the parts o IS . series of animals, we always discover some analogy, even ~ species the most remote from each other; and may trace t e gradations of one same plan from man to the last of the fishes. In the second form there is no skeleton; the muscles are INTRODUCTION. 31 merely attached to the skin, which constitutes a soft contractile envelope, in which, in many species, are formed stony plates, called shells, whose position and production are analogous to those of the mucous body. The nervous system is contained within this general envelope along with the viscera, and is composed of several scattered masses connected by nervous filaments; the chief of these masses is placed on the resophagus, and is called the brain. Of the four senses, the organs of two only are observable, those of taste and sight, the latter of which are even frequently wanting. One single family alone presents organs of hearing. There is always, however, a complete system of circulation, and particular organs for respiration. Those of digestion and secretion are nearly as complex as in the vertebrata. We will distinguish the anit:Qals of this second form by the appellation of .llnimalia Mollusca. Although, as respects the external configuration of the parts, the general plan of their organization is not as uniform as that of the vertebrata; there is always an equal degree of resemblance between them in the structure and the functions. The third form is that remarked in worms, insects, &c. Their nervous system consists of two long cords, running longitudinally through the abdomen, dilated at intervals into knots or ganglions. The first of these knots, placed over the resophagus, and called brain, is scarcely any larger than those that are along the abdomen, with which they communicate by filaments that encircle the resophagus like a necklace. The covering or envelope of the body is divided oy transverse folds into a certain number of rings, whose teguments are sometimes soft, and sometimes hard ; the muscles, however, being always situated internally. Articulated limbs are frequently attached to the trunk ; but very often there are none. We will call these animals .!lnimalia .!lrticulata, Or articulated animals, in which is observed the transition |