ZOOLOGICAL SOCIETY BULLETIN 6! 
setting it aside in a place not too light. In a 
few days a scum will form on the surface. In- 
fusoria breed slightly faster if the infusion. is 
placed in the dark than if set in the light, even 
though shielded from a glare. The mixture 
darkens as it ripens. In two days a few thou- 
sand infusoria have appeared, in four days 
myriads. In seven days their number is legion. 
As time passes they become thick an inch or two 
below the surface, and various species appear, 
including the swan, bell, and slipper animalcules. 
About the ninth day the scum may be full of 
common rotifers also. 
Rotifers are microscopic animals sometimes 
called animalcules, because no larger than pro- 
tozoa. They are properly grouped with the 
worms. Many have little shells; all are pos- 
sessed of definite organs, with an alimentary 
tract, nephridia, eyes as a rule, and are sep- 
arately sexed. 
In an infusion of dried lettuce, one may look 
for rotifers on the ninth day also, but infusoria 
are never as thick as in a hay infusion. 
Infusoria Culture —Various powdered prep- 
arations are now on the market which, when 
placed in water, generate infusoria. Use gen- 
erously, doubling or tripling the prescribed 
amount, and in six to eight days the infusion 
will be teeming with minute infusoria. 
It is hoped that our aquarist friends will not 
make the mistake made by some of the manu- 
facturers of infusoria culture, who call it “A 
culture for producing a minute water insect to 
feed baby fishes.” An insect is an organized 
animal with six legs, eyes, alimentary tract, etc., 
more highly developed than worms, starfishes, 
corals and sponges; while infusoria are one of 
the five classes of protozoa—smallest and 
simplest of all known animals, having but a 
single body cell and no organs whatever, and 
all being microscopic. 
Infusoria differ from other protozoa in that 
their bodies are provided with cilia either when 
young or throughout life. Cilia are fine threads 
of the body plasm, resembling hairs, and are 
useful for locomotion and for whirling smaller 
animals and plants into the gullet, where there 
is a gullet. Some of the protozoa merely pass 
over their food and secure it by pressing it into 
their soft bodies. They are cannibalistic, having 
no compunction about consuming their own kind 
if small enough to be engulfed. When the pro- 
tozoan’s body becomes uncomfortably fat, it 
remedies the situation by constricting itself in 
the center until it breaks apart, each half taking 
up existence as an independent animal. This 
or 
is its common method of reproduction, though it 
also reproduces by spore formation. 
Aquatic Plants——These may be packed in a 
shallow dish with a broad surface and just 
enough water to cover, and allowed to decay. 
Numerous protozoa appear within a week, and 
in ten days the largest sizes of protozoa appear 
in the surface film—paramoecia (slipper animal- 
cules), mussel animalcules, and rotifers; and 
sometimes blood worms develop, which are ex- 
cellent food for all fishes with mouths large 
enough to take them in. Blood worms are small, 
scarlet, squirming creatures, not really worms 
but the larvae of gnats having no common name. 
They are the common food of young brook trout 
in the wild state. 
It may be easy enough to understand the oc- 
currence of protozoa in decaying aquatic plants, 
since they would be living among the plants 
anyway and as the plants decayed and bacteria 
gathered in the dish the protozoans would find 
more to eat and would grow and_ reproduce 
faster. But the question may well be asked, 
Why do protozoa appear in dried hay infusion, 
or in the infusoria culture now on the market, 
which is made, probably, of dessicated grasses, 
lettuce, hay, ete. The only explanation we can 
offer of this is that protozoans and rotifers both 
have power to resist dessication; that they be- 
come encysted and blow about (eggs of rotifers 
do the same) till they strike a moist place like 
wet grass, when they break through the cyst and 
swim about, becoming encysted again when the 
grass dries. Bacteria, of which the air is full, 
would naturally appear in any of the infusions, 
and on these the protozoans and rotifers would 
feed, growing fat and reproducing more rapidly 
than if undernourished. 
NATIVE FISHES 
Our native fishes suitable for home aquaria 
are comprised principally of minnows, dace, 
sunfishes, sticklebacks, chubs, catfishes, crappie, 
eels, suckers and darters. The most showy are 
the red-bellied dace and rosy-sided minnows, 
the sunfishes, darters, and some of the Southern 
killifishes. They all live well in balanced 
aquaria except the darters, which really require 
running water and are generally short-lived in 
the home aquarium. No fish taken from a cool, 
running brook, will do as well in still water as 
those taken from ponds and lakes. 
One “happy family” tank of small native 
fishes is maintained at the Aquarium for the 
observation of those interested in collecting such 
specimens. We have been unable to keep 
darters very long in standing water, and have 
