Met·a·gen·e·sis n.
 1. Biol. The change of form which one animal species undergoes in a series of successively produced individuals, extending from the one developed from the ovum to the final perfected individual.  Hence, metagenesis involves the production of sexual individuals by nonsexual means, either directly or through intervening sexless generations.  Opposed to monogenesis. See Alternate generation, under Generation.
 2. Biol. Alternation of sexual and asexual or gemmiparous generations; -- in distinction from heterogamy.

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 Al·ter·nate a.
 1. Being or succeeding by turns; one following the other in succession of time or place; by turns first one and then the other; hence, reciprocal.
    And bid alternate passions fall and rise.   --Pope.
 2. Designating the members in a series, which regularly intervene between the members of another series, as the odd or even numbers of the numerals; every other; every second; as, the alternate members 1, 3, 5, 7, etc. ; read every alternate line.
 3. Bot. Distributed, as leaves, singly at different heights of the stem, and at equal intervals as respects angular divergence.
 Alternate alligation. See Alligation.
 Alternate angles Geom., the internal and angles made by two lines with a third, on opposite sides of it. It the parallels AB, CD, are cut by the line EF, the angles AGH, GHD, as also the angles BGH and GHC, are called alternate angles.
 Alternate generation. Biol. See under Generation.


 Gen·er·a·tion n.
 1. The act of generating or begetting; procreation, as of animals.
 2. Origination by some process, mathematical, chemical, or vital; production; formation; as, the generation of sounds, of gases, of curves, etc.
 3. That which is generated or brought forth; progeny; offspiring.
 4. A single step or stage in the succession of natural descent; a rank or remove in genealogy. Hence: The body of those who are of the same genealogical rank or remove from an ancestor; the mass of beings living at one period; also, the average lifetime of man, or the ordinary period of time at which one rank follows another, or father is succeeded by child, usually assumed to be one third of a century; an age.
    This is the book of the generations of Adam.   --Gen. v. 1.
    Ye shall remain there [in Babylon] many years, and for a long season, namely, seven generations.   --Baruch vi. 3.
    All generations and ages of the Christian church.   --Hooker.
 5. Race; kind; family; breed; stock.
    Thy mother's of my generation; what's she, if I be a dog?   --Shak.
 6. Geom. The formation or production of any geometrical magnitude, as a line, a surface, a solid, by the motion, in accordance with a mathematical law, of a point or a magnitude; as, the generation of a line or curve by the motion of a point, of a surface by a line, a sphere by a semicircle, etc.
 7. Biol. The aggregate of the functions and phenomene which attend reproduction.
 Note: ☞ There are four modes of generation in the animal kingdom: scissiparity or by fissiparous generation, gemmiparity or by budding, germiparity or by germs, and oviparity or by ova.
 Alternate generation Biol., alternation of sexual with asexual generation, in which the products of one process differ from those of the other, -- a form of reproduction common both to animal and vegetable organisms. In the simplest form, the organism arising from sexual generation produces offspiring unlike itself, agamogenetically. These, however, in time acquire reproductive organs, and from their impregnated germs the original parent form is reproduced. In more complicated cases, the first series of organisms produced agamogenetically may give rise to others by a like process, and these in turn to still other generations. Ultimately, however, a generation is formed which develops sexual organs, and the original form is reproduced.
 Spontaneous generation Biol., the fancied production of living organisms without previously existing parents from inorganic matter, or from decomposing organic matter, a notion which at one time had many supporters; abiogenesis.

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