reproduction. The coordinated 
beating of cilia in the oviduct 
produces a sort of current 
that draws the egg into the 
uterus, while the rapidly 
thrashing flagella of sperm 
help them to “swim'” toward 
the egg. 
The inherent ability of micro- 
tubules and microfilaments to 
assemble and disassemble 
rapidly allows for the construc- 
tion and destruction of these 
cytoskeletal components to 
suit the needs of a moving 
cell. In contrast, intermediate 
filaments are the most stable 
of the cytoskeletal fibers. At 8 
to 10 nanometers in diameter, 
they are intermediate in size 
between microfilaments 
and microtub ides. Intermediate 
fdaments are strong and are 
found in cells that require or 
provide mechanical strength, 
such as those of the skin and 
intestines. It is believed that 
these filaments also have 
other important functions in 
cell physiology, and researchers 
are studying the cause and 
effect of their alteration 
during disease. 
Current investigations of the 
cell’s organelles — the nucleus, 
ribosomes, endoplasmic 
reticulum, Golgi apparatus, 
lysosomes, peroxisomes, 
mitochondria, and cytoskele- 
ton — hold great promise for 
the solution of problems in 
basic biology and clinical 
medicine. However, the key 
that may unlock the greatest 
number of health benefits 
may well be found in the 
cell’s filmy membranes, 
particularly the surface mem- 
brane, which plays a pivotal 
role in maintaining the 
integrity of the cell and, in a 
larger way, in protecting the 
health of the organism. 
Some microorganisms 
are equipped with a 
flagellum ( composed of 
microtubules), which 
thrashes to propel the 
animal. 
