Reproduction Definitions

Taken from Funk & Wagnalls Encyclopedia as provided on the InfoPedia CD-ROM.  Emphases supplied.

Asexual Reproduction

Most single-celled organisms reproduce by a process known as fission, in which the parent organism splits into two or more so-called daughter organisms, thereby losing its original identity. Cell division, which results in the multiplication of cells constituting the tissues, organs, and systems of a multicellular organism, is not considered true reproduction; it is almost identical, however, with the binary fission of single-celled organisms. In certain multicellular animals, such as the coelenterates, sponges, and tunicates, cell division often results in the production of buds that arise from the body of the parent and then later separate to develop into a new organism identical with the parent; this process, known as gemmation, is analogous to the process of vegetative reproduction or propagation in plants.  Reproductive processes such as those cited above, in which only one parent gives rise to the offspring, are scientifically classified as asexual reproduction.  The offspring produced are identical with the parent.


In some relatively simple animals such as the earthworms and leeches, organs producing sperm and ova occur in the same individual (see Hermaphroditism details below).  Although such animals produce both male and female gametes, the production of sperm and ova usually occurs at different times, so that these animals generally do not fertilize themselves but rather other individuals of the same species.  Certain hermaphroditic animals, such as the planarian flatworms, habitually undergo self-fertilization. Among plants, one individual may bear reproductive organs of only one sex, separate reproductive organs of both sexes, or reproductive organs containing both male and female elements ( see Flower ). Individuals among higher animals bear reproductive organs of only one sex.



In biology, the presence in one individual, plant or animal, of both male and female gonads or organs of sex cell production. The term is derived from the legend of Hermaphroditus (q.v.) .

Hermaphroditism occurs in the great majority of flowering plants: Monoclinous plants have hermaphrodite, or perfect, flowers, each of which has both male and female elements (stamens and carpels); monoecious plants have flowers containing only male elements and others containing only female elements, both occurring on the same plant. Only a few flowering plants are dioecious, that is, carrying male and female organs on different plants. Most hermaphroditic plants produce male and female elements at different times to ensure cross-pollination; a few, such as the violet and the evening primrose, are habitually self-pollinated.

Hermaphroditism habitually occurs in many invertebrate animals, in the hagfish and tunicate, and in the sea bass of the genus Serranus. It occurs occasionally in other fishes, in frogs, toads, and certain newts among the amphibians.  Hermaphrodite animals are rarely self-fertilizing; in most cases the spermatozoa and ova mature at different times (successive hermaphroditism), or the male and female external organs are located so that self-fertilization is impossible. Among the invertebrates, sponges, coelenterates, some mollusks, and earthworms are regularly hermaphroditic.  Flatworms have a complete set of male and female gonads in each segment and regularly fertilize themselves.

True functional hermaphroditism is rare or absent in higher animals. One occasionally sees animals called hermaphrodites that appear intermediate in form between males and females, but such animals are usually sterile, and, when fertile, do not produce both fertile eggs and fertile sperm. Such organisms are often called intersexes or sex-intergrades; intersexes in the fruit fly have been shown to arise from inheritance of an abnormal ratio of male Y chromosomes to female X chromosomes ( see Genetics ). Human pseudohermaphrodites show functional disturbance of the endocrine glands, especially of the pituitary or adrenal glands, and do not possess two sets of functioning sex organs. Because of the homology between male and female sex organs, it may be difficult to tell whether a human hermaphrodite is a female with overdeveloped clitoris or a male with underdeveloped penis, cleft scrotum, and nondescendant testes. Recently, many persons have undergone surgical or hormone treatment to modify their nonfunctioning sex characteristics and emphasize the sex indicated by those that are functional.

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