A "morph," or "metamorph," is described in the standard docs as the
type of race you'd see in John Carpenter's "The Thing." The major
differences between morphs and normals can be summarized like this:

   -- Morphs can absorb enemy bodies when they attack a sector
   -- Morphs can build spore pods on planetary surfaces
   -- Morphs' IQ is determined only by their population

It used to be the case that morphs had a very high metabolism and very
high fighting strength to go along with all of this, but the advent of
racegen has changed that considerably. Now, morphs can have all of the
basic characteristics of normal races -- but the three attributes
mentioned above are only available to metamorphs. The disadvantage
that offsets this option is that some items will be more expensive in
racegen.

I'll discuss these three items in reverse order: First, morph IQ is
based on some exponential population formula. In all games, this means
their IQ starts at 0, and the maximum possible morph IQ can be set by
the player in racegen. A common practice is for morphs to spend a
great deal of tax money investing in tech to offset this disadvantage,
but it still takes a while to "take off." The low IQ means that morphs
cannot rely on shuttles (which require some minor tech ability to
build) to ferry them around to colonize planets early in the game.
Morphs, however, have the ability to build spore pods. These pods
require no tech to build and are very cheap.

The major advantage to spore pods is this low cost and the fact that
they can be built right on the planet's surface (while most other ship
types require factories which need resources to be turned on and time
to repair before actually building any ships). The drawbacks to pods
are that they are slow and that they explode upon entering star
systems. That's not _always_ a drawback, but early in the game, it
will mean that several pods must be sent to a system in order for you
to have a good chance at landing morphs on a planet or two. The
success rate of spore pods (ie. whether they explode harmlessly or
result in a colony) varies from game to game from 20% to 40%.

The other major difference between morphs and normals which is
mentioned above is morphs' special combat ability. If a morph attack
force defeats another race in ground combat, a large fraction of the
defeated enemy will be "absorbed" by the attacking morph race,
enabling morphs to actually _increase_ their population through
attacking. Thus, late in the game when all planets are covered and
well-defended by other races, morphs still have a chance to do some
serious damage by showering an enemy system with pods and perhaps
landing enough morphs in the system to cause a lot of problems, if not
to take over a planet or two.