RECREATIONS™MICROSCOPE 
The Wheel An’malcules. 
BY DR. E. BADE, IN “AQUATIC LIFE.” 
Among the minute animals which 
people the water, the rotifers or 
“wheel bearers,’’ Rotatoria, form a 
very interesting class. Only a few 
of them reach even three millimeters 
in length, and they are giants of the 
race ; usually they vary between one- 
BRACHIONUS URCEOT ARTS. MET TCERTA 
RINCENS AND STF.PTT AXOCEROS 
EICHHORNI. 
twentieth and one-tenth mm. in 
length (a millimeter is approximately 
one twenty-fifth of an inch.) These 
little 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 instance. A few live in the 
sea; some, in the intestines of worms 
and molluscs, lead parasitic lives, but 
the species most numerous are those 
that prefer the quiet backwaters of 
streams, the bottoms of plant-grown 
ponds or the puddles in swamps. One 
family, the Bdelloidae, occurs 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 persisted. The anterior end of the 
body carries a retractile ciliated ap- 
paratus, the so-called “wheel organ,” 
which varies considerably in appear- 
ance in the different species. This or- 
gan, thickly beset with cilia, has a two- 
fold purpose, serving for locomotion 
and also creating a current in the wate~ 
whereby edible substances are brouglu 
to the ever hungry maw. The “wheel” 
appears circular for one moment, es- 
calloped 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 
appearance is so deceptive that the first 
observers assumed 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 animals 
are being examined microscopically the 
cilia play 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 system is not quite clear. 
Ehrenberg classed them as “Infu- 
soria,” but that was a century ago, 
when the unicellular animals, the Pro- 
tozoa, were not definitely understood. 
Similar looking creatures were grouped 
together, and as one-celled ciliated in- 
fusoria frequently recall many rotifers 
in appearance, all were promptly put 
together as of one relationship. Today 
the rotifers are classed near the worm'. 
