Many simple multicellular animals produce offspring by budding, in which new individuals form as outgrowths of the bodies of older animals. A bud grows by mitotic cell division, and the cells differentiate before the bud breaks away from the parent (Figure 43.1a). The bud is genetically identical to the parent, and it may grow as large as the parent before it becomes independent.
Regeneration is usually thought of as the replacement of damaged tissues or lost limbs, but in some cases pieces of an organism can regenerate complete individuals. Echinoderms, for example, have remarkable abilities to regenerate. If sea
43.1 Asexual Reproduction in Animals (a) Budding: A new individual forms as an outgrowth from an adult hydra. (b) Regeneration:This five-armed sea star is generating three new arms to replace amputated limbs ones,form-ing a complete animal.
stars are cut into pieces, each piece that includes a portion of the central disc grows into a new animal (Figure 43.1b).
Regeneration frequently results when an animal is broken by an outside force. A storm, for example, can cause a heavy surf that breaks colonial cnidarians such as corals. Pieces broken off the colony can regenerate into new colonies. In some species, the breakage occurs in the absence of external forces. Some species of segmented marine worms related to the ones we discussed at the beginning of this chapter develop segments with rudimentary heads bearing sensory organs, then break apart. Each fragmented segment forms a new worm.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.