Distinction between the Kingdoms of Nature--Progress of Animal Life--Sponges--Polypes--Infusoria--Animalcula--Phosphorescent Animals--Annelidans--Myriapoda--Animal Metamorphoses--Fishes--Birds--Mammalia--Nervous System--Animal Electricity--Chemical Influences--Influence of Light on Animal Life--Animal Heat--Mechanical Action--Nervous Excitement--Man and the Animal Races, &c. “A stone grows; plants grow and live; animals grow, live, and feel.” Such were the distinctions made by Linnæus, between the conditions of the three kingdoms of nature. We cannot, however, but regard them as in all respects illogical. The stone--a solid mass of unorganized particles--enlarges, if placed in suitable conditions, by the accretion of other similar particles around it; but it does not, according to any meaning in which we use the word, _grow_. Plants and animals grow; and they differ, probably, only in the phenomena of sensation. Yet, the trembling mimosa, and several other plants, appear to possess as much feeling as sponges and some of the lower classes of animals. By this definition, however, of the celebrated Swedish naturalist, we have a popular and simple expression of a great fact. As we have only to examine the question of the agency of the physical forces upon animal life, we must necessarily confine our attention to the more striking phenomena with which science has made us acquainted; and, having briefly traced the apparent order in which the advance of organization proceeded, we must direct our few concluding remarks to the physico-physiological influences, which we must confess to know but too imperfectly. We learn that, during the states of progress which geology, looking into the arcana of time, has made us acquainted with, a great variety of animal forms were brought into existence. They lived their periods. The conditions of the surface of the earth, the sea, or the atmosphere, were altered; and, no longer fitted for the enjoyments of the new life, these races passed away, and others occupied their places, which, in turn, went through all the stages of growth, maturity, and decay; until at length, the earth being constituted for the abode of the highest order of animals, they were called into existence; and man, the intellectual monarch of the world, was placed supreme amongst them all. Types of nearly all those forms of life which are found in the fossil state are now in existence; and if we examine the geographical distribution of animals--the zones of elevation over the surface of the earth, and the zones of depth in the ocean,--we shall find, now existing, animal creations strikingly analogous to the primitive forms and conditions of the earth’s inhabitants. From the depths of the ocean we may even now study--as that most indefatigable naturalist, Professor Edward Forbes, has done--the varying states of organization under the circumstances of imperfect light and varying temperature.[261]