Reproductive duality

Many animals, particularly the lower metazoans, actually use both asexual and sexual reproduction at various times. This reproductive duality gives them the advantages of both modes. It is rare for both asexual and sexual reproduction to occur simultaneously, however. In many lower metazoans, the asexual and sexual processes are cyclical, occurring in different seasons. Examples include many marine sponges (phylum Porifera), in which a single individual may alternate between reproductive modes. Another example may be seen among the freshwater rotifers (phylum Rotifera), in which the two reproductive modes will be restricted to sequential generations that are otherwise anatomically similar. In other lower meta-zoan groups, asexual and sexual processes are segregated into two distinct stages in the life history, with radically different anatomical and behavioral traits, or even different habitats. The best examples of these stages are found among the hy-droids and jellyfishes (phylum Cnidaria), and among the parasitic flatworms (phylum Platyhelminthes). Since the life history stages responsible for asexual and sexual phases are so distinctive in these groups, and occur in a regularly alternating pattern, this general reproductive strategy is often called alternation of generations.

Essentials of Human Physiology

Essentials of Human Physiology

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.

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