kuento@kuhub.cc.ukans.edu (10/21/90)
In article <20590@ttidca.TTI.COM>, jackson@ttidcc.tti.com (Dick Jackson) writes: > Sometimes I watch ants and even smaller creatures moving about on their > tiny legs. It makes me wonder whether these little guys have hearts and > livers, muscle and tendons, fat, etc. just like I have. > > I suppose they must have at least primitive versions of these. My > question is: Can the little devils, e.g. mites, be dissected and their > structures analysed? Also, what is the smallest creature that walks on > legs? > > Dick Jackson The internal organization of Arthropods is considerably different from ours, what with their "skeletons" on the outside, but there are some similarities, for sure. To simplify, if you dissect an ant, all you will see loose in the body cavity is a digestive tract, and if it's a male or a queen, some gonads. They have no kidneys - excretion is the job of hairlike structures attached to the digestive tract (Malpighian tubules). No livers, no spleens, no pancreas...they have what is called a "heart", but it is only a muscular tube, open at both ends (and with rows of openings along the side) which helps to circulate the fluid in the body cavity, called hemolymph (this arrangement is called an open circulatory system). Nerves run along the body wall, and muscles insert on the exoskeleton - insects also possess a very special type of muscle (used for flight) known as "asynchronous", because it can contract several times for each incoming nerve impulse, unlike our muscles with their one-for-one response (that's one of the tricks that lets Bumblebees fly when wives' tales say otherwise). So much for the cheap tour of an ant. The smallest true Insects are on the order of 0.1 mm, but if you broaden it to all Arthropods, then mites and tardigrades (water bears) are the tiniest. I'm not so certain that tardigrades ever "walk", in the sense of walking on a dry surface, but they have legs, and are measurable in microns. The mites that live on human bodies are in the same general size neighborhood (you know, bed mites, scalp mites, and the ones that live inside your eyelashes?). It's easier to see the Space Shuttle in orbit with the naked eye than it is to see these little critters...gee, ain't Nature amazing? 8-) ---------------------------------------------------------------- Doug Yanega (Snow Museum, Univ. of KS, Lawrence, KS 66045) My card: 0 The Fool Bitnet: Beeman@ukanvm Disclaimer? Ha! Have opinion, will travel...