It is clear however that no single detractor is sufficient to mark the line between those two kingdorruk, and that the collective functions performed by animals and plant& as they are more or less prominent In organised beings, guide the opinions of naturalists. The structural characters of typical animals are so evidently different from the corresponding forms of plants, that we need not dwell on them here ; but a view of the functions which animals and plants perform dependently on one another, will give the best possible notion of their antagonistic nature. Ono of the great functions performed by the animal kingdom is that of Respiration. During this process the oxygen of the atmosphere is brought in contact with carbon in the blood of the animal, and the result is a union of the carbon and oxygen, and the formation of carbonic' acid gas, which is being constantly thrown off from the structure of the animal—from the whole surface of the body in the lowest animals, from the gills of those that live in water, and from the lungs of those that live in air. It thus consumes oxygen and gives of carbonic acid. The great function of plants is antagonistic to this. They take from the air carbonic acid gas ; it is a part of their food. In the tissues of the plant the carbonic acid is decemixeel Its elements are separated ; the carbon is retained in the plant, anti tho oxygen is set free. It thus consumes carbonic acid and gives off oxygen. As far as we at present know there are no exceptions to this law. On tracing the supply of the carbon which is contained in the animal system, and which combines with the oxygen, we find that it is derived by the animal from the plant. The food of the whole animal kingdom is derived from the vegetable kingdom ; and the other three elements, as well as the carbon, which are found in the animal, are thus obtaine t The animal, in like manner, throws off its nitrogen in the 'oral of excretions, more especially those of the kidneys, which, on decom posing, yield nmmonia, a compound of nitrogen and hydrogen ; end it is from this substance that plants principally derive their nitrogen. Thus, whilst the animal derives the constituent of its body from the vegetable kingdom, the plant derives its elements from the mineral kingdom. The animal takes up starch, sugar, and protein, from the plant, but the plant takes up carbonic acid and ammonia in their mineral form. The tissues of the plant are engaged in converting mineral into organic substances, whilst the tissues of the animal are engaged in converting organic substances into mineral.
In their relation to the great phyaicaLforces, heat and light, we ace the same antagonism between plants and animals. Light and heat are essential to the growth of plants. The productions found iu their tissues are but the expression of the amount of heat and light they have as it were appropriated. Many of the substances thus formed are taken into the system of animal's as food; and whilst in the system of the animal, the heat and the light are again set free in the form of the peculiar vital animal forces.
It is then by regarding the Animal and Vegetable worlds as exhibiting a combination of antagonistic and dependent forces in the great circle of nature, that we shall best form an idea of the real difference's that exist between these two kingdoms of nature. Having said this much
with regard to the nature of the Animal Kingdom, we shall now proceed to consider some of the methods which have been employed by naturalists to arrange the various members of which it is com posed into groups, for the purpose of exhibiting the relation of one animal to another, and of facilitating the study of the whole.
In a crude shape, zoology, or the arrangement of animals, most have been one of the earliest sciences that forced itself upon the attention of the human mind. The very necessity for finding names for the more obvious divisions of living beings must soon have produced a classification into the natural groups of Quadrupeds, Birds, Fishes, and Insects; and certain subordinate sections, as, for instance, the distinction between herbivorous and carnivorous beasts, granivorous and 'carnivorous birds, harmless and poisonous reptiles, must have followed as a matter of course.
We have in the Bible, and in the engraven and pictorial Egyptian records, the earliest evidence of the attention which had been paid to Natural History in general. The ' navy of Tarshish ' contributed to the wisdom of him who not only "awake of the trees, from the cedar of Lebanon even unto the hyssop that springeth out of the wall," but "also of beasts, and of fowl, and of creeping things, and of fishes" (1 Kings iv. 10); to say nothing of numerous other passages showing the progress that zoological knowledge had already made.
The Egyptian records bear teatiniony to a familiarity not only with the forms of a multitude of wild animals, but with their habits and geographical distribution.
Although it must ho admitted that Herodotus was behind the science of his day in physical knowledge, lie who, despising the sneers of the half-learned nt his wonderful stories, will bring to the perusal of his works a fair share of scientific acquirement, will find many instances of zoological information which have been taken for the mere tales of tide excellent traveller and historian, but which modern investigation has confirmed. But it is to Aristotle, justly termed the father of natural history, that we owe the first dawning's of system founded on the only sure basis--the organisation or physio logical character of animals.
Aristotle's method was founded on a division of organs, which may be arranged, first, with reference to natural groups (Karat or ecre filer), Birds or Fishes, for instance, which depend on a similar structure of parts; secondly, accotsling to their excess and defect (Kae inrEpoxby Kai faaseple), as, for example, a division of Birds into those with long bills and those with short bilks; those having crest's and those having none; thirdly, according to their nnalogion (scar' avaicryfav); take, for instance, time comparison of a hoof with a claw, the wing of a bird with the fore-foot of a quadruped, a feather with a scale ; and, fourthly, according to their situation (sank eiaim); take, for example, animals which !Inv° pectoral mammas man, apes, and elephants; mid animals which have abdominal mammas : dogs and cats.
The writers who succeeded Aristotle, and mostly copied from his ample stores were : .zElian, Pliny, Athenmus, Albertus Magnus, Belon, Gesner, Aldrovandus, and Johnston. Although some of them recorded new facts they did nothing to supply any further arrangement of the animal kingdom.