The Little Fellows with 

 the "Wheel" 



DR. K. BADE. New York 



Ainoii<>- the niimitf animals wliicli jicoph' 

 the wattr, tlu' Ilotiftr.s or "wlutl hear- 

 ers" form a vi-ry interesting chiss, only a 

 few of them reach even three millimeters 

 in length and they are giants of the race. 

 They usually vary hetween one-twentieth 

 and one-tenth nnn. in length. These little 

 fellows put dramatic movement into the 

 life of the })ond. Some sport around in 

 the clear water^ "Knights of the Lists," in 

 armor clad^ bear mighty lances as do others 

 thorns. Some are sessile on the plants, for 

 instance, under the lily pads. A few live in 

 the sea; some, in the intestines of worms 

 and mollusks lead parasitic lives, but by 

 far most numerous are those that prefer the 

 quiet backwaters of streams, the bottoms 

 of plant-grown ponds or the puddles of 

 swamps. One family of them, the Bdelloidae, 

 occurs in the moss of house-roof's, and in the 

 lichen-growths of tree-trunks or rocks. 



W^heel animals the older naturalists named 

 them and this name they still bear. The 

 anterior end of the body carries a retractile 

 ciliated apparatus, the so-called "wheel- 

 organ," which is of very variable appearance 

 in the different species. This organ 

 thickly beset with eiliie is used for a 

 two-fold purpose, for locomotion and also 

 tor creating a current in the water where- 

 by edible substances are brought to the 

 ever hungry maw. The "wheel" looks 

 circular for one moment, scalloped the next, 

 then frilled, lobed, even-branched or arm- 

 like. Under a powerful glass this ceaseless 

 play of the ciliae looks like the turning of 

 the spokes of a wheel. This appearance 

 is so deceptive that the first observers as- 

 sumed it as a fact that the animals carried 

 a wheel, hence the name. 



By adding a little cocaine or quince-gum 

 to the water in which the animal is ex- 

 amined microscopically the play of the 

 cilite slackens and thus it is jjlainly to be 

 seen that there is no wheel in motion, but 



simply little hairs (the ciliae) which 

 rhytlnnically beat the water. But the little 

 wheel organ is not the only thing of inter- 

 est with these fellows. Even now their 

 exact position in the zoological system is 

 not quite clear. 



Ehrenberg classed them as "Infusoria." 

 That was about a hundred years ago when 

 the unicellular animals, the Protozoa, were 

 not definitely known. Similar looking 

 creatures were simply classed together, and 

 as one-celled ciliated infusoria frequently 

 recall many rotifers in appearance, all were 

 ])romptly put together as of one relation- 

 ship. Today the rotifers are classed with the 

 ii'onns — that great class of animals which 

 still has to serve as a catch-all to the zoolo- 

 gist. Here is placed everything which 

 cannot be elsewhere put. We know that 

 these animals are many-celled and highly 

 organized, and offer as an excuse for their 

 position among the Worms their affinities of 

 type with certain larval forms of the 

 Trochophora tjqje. In them the cilia are at 

 first much developed, but in the end are 

 restricted to certain localities of the body, 

 one of which appears constant about the 

 mouth. Hence the conclusion that our roti- 

 fers are exceedingly primitive forms with 

 close relations to the progenitors of the 

 phylum or genealogical tree of the Vermes 

 (Worms). 



The Rotifers have a motile dental appa- 

 ratus, a stomach of many cells, an intestine, 

 salivary and renal glands, brains and 

 nerves and red ejes. The microscope re- 

 veals all these organs in operation. You 

 seem to look through a window at a delicate 

 clockwork, so transi)arent is the skin of 

 most of them. Manifold are their shapes. 

 Free swimmers have balancers and other 

 attachments assisting them in floating and 

 swimming. Most of the sessile ones con- 

 struct protective casings of foreign ma- 

 terial (Mcliccrta) , or exude a jelly-like 

 covering (Floscularia). Others simply are 

 attached by a pedicel ending in a sucking 



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