ZOOLOGY. 



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ZOOLOGY (from Greek soon, an animal, and 

 logos, a discourse) treats of the form and 

 structure of animals, and the characters by which 

 they may be distinguished from each other. 



All natural bodies may be divided into two great 

 groups mineral or inorganic, and living or organic. 

 The organic are again subdivided into -vegetables 

 and animals. Hence arises the division of all 

 natural objects into three great kingdoms namely, 

 the Mineral, Vegetable, and Animal. 



Inorganic substances never live. Chemically, 

 they may be simple or compound, such combina- 

 tions usually forming binary or ternary compounds. 

 Their physical condition may be solid, fluid, or 

 gaseous ; but they are homogeneous in texture, 

 that is, any detached portion exactly resembles 

 the remainder in composition and properties. 

 They may be amorphous, without distinct forms ; 

 or crystalline, that is, having distinct geometrical 

 forms, bounded by plane surfaces, which have a 

 definite relation to each other. They increase by 

 the addition of like particles to their surface, which 

 is termed accretion or juxtaposition. Their atoms 

 are at rest, unless set in motion by some physical 

 force acting from without : they initiate no change 

 or motion. 



An organic being either lives or has lived during 

 some part of its existence. Chemically, it con- 

 sists of few elements, which unite to form ternary 

 and quaternary compounds. It consists of solid 

 and fluid parts, which exercise a reciprocal action 

 on each other. It is bounded by curved lines, 

 and has convex and concave surfaces. Each 

 organised being, under the influence of life, 

 assumes a characteristic, though not absolutely 

 definite shape. It increases or grows by receiving 

 into its interior matter which it elaborates and 

 assimilates. The old particles are being con- 

 stantly removed, and replaced by new ones, so 

 that all its parts are in constant motion, and are 

 ever changing. It arises from some pre-existing 

 organism of the same kind, by means of a germ, 

 which becomes separated, and enjoys an individual 

 existence. 



We do not know ' life ' apart from matter ; some 

 material substratum or ' physical basis ' is required 

 for its manifestation. This, according to Huxley, 

 is furnished by what he calls protoplasm, which 

 is a homogeneous, structureless substance, en- 

 dowed with contractility, and having a chemical 

 composition nearly allied to that of albumen : it is 

 composed of carbon, hydrogen, oxygen, and nitro- 

 gen. This term life indicates a very special prop- 

 erty indeed ; and at present, looking at it from a 

 purely material point of view, we are scarcely justi- 

 fied in regarding life as more than that condition 

 of an organised being in which the products of 

 chemical and physical changes taking place within 

 it are stamped with a specific form. By the term 

 * moulding of specific form ' is meant the building 

 up of a complicated and heterogeneous organism, 

 which repeats the characters which have been 

 transmitted to it through a germ, by a parent, 

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every molecule of every part having thus a direct 

 relation in form, in position, and in composition, 

 to every other molecule of the body. 



It is impossible to draw a distinct line of de- 

 marcation between vegetables and animals, as 

 the lowest forms of both kingdoms seem to meet 

 and merge into each other. It was on this account 

 that Professor Ernst Haeckel of Jena constructed 

 a fourth kingdom, called by him 'Protista,' into 

 which he proposed to put all the organisms of 

 doubtful affinity. But this, at present, seems 

 scarcely justifiable. Of course, the conspicuous 

 members of the vegetable kingdom can never be 

 confounded with the higher animal forms. In 

 the latter, the presence of a nervous system, the 

 possession of a mouth and digestive cavity, as well 

 as the power of voluntary locomotion, are sufficient 

 to distinguish them from the former, in which all 

 these are absent. In the simplest groups in each 

 kingdom, however, these grand distinctions are 

 lost. Chemically, plants consist chiefly of ternary 

 compounds that is to say, compounds consisting 

 of three elementary ingredients, as starch and cellu- 

 lose, which are different combinations of oxygen, 

 hydrogen, and carbon. In an animal, quaternary, 

 and still more complex compounds, as albumen, 

 fibrine, and gelatine, make up the bulk of the 

 body ; while ternary compounds, though, indeed, 

 not wanting, play a subordinate part. The general 

 plan of nutrition is strongly contrasted in the 

 two kingdoms ; but in some low animal forms, 

 as the Gregarinae, nutrition is effected by absorp- 

 tion through the external surface, just as is the 

 case in plants. Most plants are permanently fixed 

 in the ground by roots, but some low forms of 

 algae are locomotive ; and although most animals 

 can move about from place to place, others are 

 incapable of progression, as the branched and 

 tree-like sponges. It may be said, in a general 

 sense, that organs of relation are present in 

 animals, and absent from plants. But some 

 phenomena connected with climbing plants, and 

 with the process of fertilisation, are very difficult 

 to explain without admitting some low form of a 

 general harmonising and regulating function, com- 

 parable to such an obscure manifestation of reflex 

 nervous action as we have in Sponges and other 

 animals in which a distinct nervous system is 

 absent 



Plants can secrete and store in their leaves 

 and other parts a substance called ' chlorophyl,' 

 by means of which, under the influence of light, 

 they absorb carbonic acid from the atmosphere, 

 decompose it, and, when the carbon is in a 

 nascent state that is, just liberated from com- 

 bination can combine it with the elements of 

 water (hydrogen and oxygen), or with the ele- 

 ments of water and ammonia, likewise reduced 

 to a nascent state by the same agency. The 

 plant thus gains from the air and from the soil 

 certain elementary substances, chiefly carbon, 

 oxygen, hydrogen, and nitrogen. These, under 

 the guidance of a vital property, and through the 



