Anatomy and physiology

 

All organisms, whether plant or animal, must reproduce, grow, breathe, eat, excrete, and be able to respond to their environment. Various systems in animals’ bodies accomplish these tasks. These systems may vary from species to species, but the chemical processes involved in the activities are usually the same.
Differences in anatomy, or arrangement of limbs and organs, have arisen for several reasons. One is that for early aquatic animals to evolve into more advanced forms that could live on land, various physical features had to be modified. For example, legs and feet replaced fins; and lungs, which enabled animals to get oxygen directly from air, replaced gills.
One of the most important anatomical developments in animals is segmentation, first seen in the earthworm, in which the body is divided into ringlike segments. The more primitive animal phyla lack segmentation, which occurs in all higher groups. In the more advanced animals, such as vertebrates, segmentation occurs only in the embryo stage.

The greater gliding possum glides from one tree-top to another on a membrane that stretches from its neck to its feet. This structural adaptation to its heavily forested environment enables the animal to get around without having to run down one tree and climb up another.

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