Blackworms are ideal organisms for studying segmental regeneration,
developmental pattern formation, and developmental transformation of
original body segments (a process called morphallaxis). Small fragments of
the worm, some only a few segments in length, can be easily amputated,
isolated, and stored using only basic lab supplies, such as a razor blade,
filter paper disk, disposable plastic pipette, and storage containers (for
example, capped centrifuge tubes or multiwell culture dishes).
Students soon discover that survival rates of body fragments are
excellent, and the regeneration of missing parts occurs quickly. For
example, development of a head (usually 8 new segments in length) and/or a
new tail (ranging from 20 to 100 or more segments in length) is usually
completed over 23 weeks (Fig. 2). Using a stereomicroscope, students can
count and readily distinguish new segments from the older, original
segments in the fragment.
Remarkably, the entire process of head and tail regeneration by a small
body fragment can be played out within a small, tightly sealed container
with as little as 12 mL of water and no food. I have continually kept
isolated worm fragments alive under these conditions for more than 6
months. Such fragments gradually diminish in size, new segments readily
regenerate. Because of their small size and pale color, the new segments
can be easily distinguished from the older ones.
2 (a) Image of newly regenerated
head and tail ends from a 16-segment -long fragment.
2 (b) Enlarged image of newly regenerated head.
Carolina Biological Supply Compagny, Article used by permission