. Essentials of biology presented in problems. Biology. XXII. THE VERTEBRATE ANIMALS Increasing Complexity of Structure and of Habits in Plants and Animals. — In our study of biology so far we have attempted to get some notion of the various factors which act upon and interact with hving things. We have learned something about the various physiological processes of plants and animals, and have found them to be in many respects identical. We have examined a number of forms of plants and have found all grades of complexity, from the one-celled plant, bacterium or pleurococcus, to the complicated
. Essentials of biology presented in problems. Biology. XXII. THE VERTEBRATE ANIMALS Increasing Complexity of Structure and of Habits in Plants and Animals. — In our study of biology so far we have attempted to get some notion of the various factors which act upon and interact with hving things. We have learned something about the various physiological processes of plants and animals, and have found them to be in many respects identical. We have examined a number of forms of plants and have found all grades of complexity, from the one-celled plant, bacterium or pleurococcus, to the complicated flowering plants of considerable size and with many organs. So in animal life the forms we may have studied, from the Protozoa upward, there is constant change, and the change is toward greater complexity of structiu-e and functions. A worm is simpler in structure than an insect, and in many ways, especially by its actions, shows that it is not so high in the scale of life as its more lively neighbor. We are already awake to the fact that we, as living creatures, are better equipped in the battle for life than our more lowly neigh- bors, for we are thinking creatures, and can change our surroundings at will, while the lower forms of animals are largely con- trolled by stimuli which come from without; tem- perature, moisture, light, the presence or absence of food, — all these result in movement and other re- actions. In structure we also differ. Particularly is this difference seen in the skeleton. We call ourselves vertebrates, because we have a 274. Cross section through (I) an invertebrate ani- mal and (V) Si vertebrate animal: a, food tube; h, heart; c, vertebrate column; n, central nerv- ous Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hunter, George William, 1873-1948. New York, Cincin
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
