A common
flatworm that lives in moist soil and fresh water. Many
species are
hermaphroditic, reproducing sexually. Most
species range in size from 1/8 of an inch to an inch, but there are
tropical forms which can grow as large as two feet long.
Planaria have eye spots that are sensitive to the presence of light, but do not
see images. One
species that is commonly studied is Dugesia tigrina.
Dugesia tigrina and similar
species can reproduce
sexually or
asexually. To reproduce
asexually, it anchors the back half of its body while the front half moves forward. This leads to it's body being
broken in half. Each end regenerates it's missing end.
On a side note, in high school
biology I did an
experiment on the effects of
caffeine on the rate at which
planaria reproduced
asexually. The results were
inconclusive and terribly
unscientific, but it did seem that the
caffeinated group split slightly more often than the
control group. For other studies on planarian worms of
dubious scientific integrity, see:
the ability of planarian worms to run a maze more successfully after being fed the remains of a successful worm.