File:Aquatic life (1918-1919) (19560719739).jpg

Title: Aquatic life
Identifier: aquaticlife419181919baus (find matches)
Year: 1918-1919 (1910s)
Authors: Bausman, Joseph E
Subjects: Aquariums; Fish culture
Publisher: Philadelphia : J. E. Bausman
Contributing Library: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library
Digitizing Sponsor: Harvard University, Museum of Comparative Zoology, Ernst Mayr Library

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n"he Wheel Animalcules DR. E. BADE Among the minute animals which peo- ple the water, the rotifers or "wheel bearers," Rotatoria, form a very inter- esting class. Only a few of them reach even three millimeters in length, and they are giants of the race; usually they vary between one-twentieth and one-tenth mm. in length (a millimeter is approximately one twenty-fifth of an inch). These lit- tle fellows put dramatic movements into the life of the pond. Some sport around in the clear water, "Knights of the Lists," bearing mighty lances, as do others thorns. Others are sessile on plants, on the lower surface of lily pads, for in- stance. A few live in the sea; some, in the intestines of worms and molluscs, lead parasitic lives, but the species most nu- merous are those that prefer the quiet backwaters of streams, the bottoms of plant-grown ponds or the puddles in swamps. One family, the Bdelloidae, oc- curs in the moss of house-roofs and in the lichen-growths of tree-trunks and rocks. The older naturalists called them wheel animals, and this popular name has per- sisted. The anterior end of the body car- ries a retractile ciliated apparatus, the so- called "wheel organ," which varies con- siderably in appearance in the different species. This organ, thickly beset with cilia, has a twofold purpose, serving for locomotion and also creating a current in the water whereby edible substances are brought to the ever hungry maw. The "wheel" appears circular for one mo- ment, escalloped the next, then frilled, lobed, even branched or armlike. Through a compound microscope the ceaseless play of the cilia gives the impression of the spokes of a revolving wheel. This ap- pearance is so deceptive that the first ob- servers assumed it as a fact that the ani- mals carried a wheel; hence the name. By adding a little cocaine or quince- gum to the water in which the animals are being examined microscopically the
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Brachionus urceolaris, Melicerta ringens and Stephanoceros eichhorni play of the cilia slackens, and it can then be seen that the apparent wheel in motion is simply very minute hairs (the cilia), which rhythmically beat the water. But the little wheel organ is not the sole point of interest with these fellows. Even now their exact position in the zoological sys- tem is not quite clear.

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