108 
Aquatic Lite 
ture is due to varying food supply. How- 
ever, the best authorities think it due to 
a change in environment. Most of our 
readers hold with the latter authorities. 
he difference in water—acidity, salinity 
or alkalinity—or the difference in the 
character of the river bed, pond bed, or 
aquarium bottom, is probably the true 
explanation of these differing sections of 
the shell. 
The periostracum, or epidermis, is a 
thin, skin-like substance, covering the 
shell. [The color of the shell is in this 
OD & os 
Acella  Galba Galba Galba 
haldemani caperata parva allt 
Bulimnea 
all nea 
5 the g asoma 
agnalis 
Six Members of the Family Lymnaedae 
epidermis. When it is removed the shell 
becomes chalky. In a clean aquarium, a 
shell will be bright, clear yellowish or 
brownish. When taken from a pond with 
a muddy bottom, with abundant decay- 
ing vegetation, it is almost black. In 
nature, shells range from dark brown to 
almost waxy white. One much eroded at 
the spire indicates acidity locally present 
in the water. 
When a snail crawls, he leaves a trail 
of mucus behind him. A large four- 
horned snail, having escaped from a tank 
for some reason undiscovered, was traced 
across the room by a trail of shiny mucus. 
Some snails can crawl, shell downward, 
on the surface film of the water. The 
Paper Shell can sometimes be observed 
doing this. Other snails spin threads and 
suspend themselves from a plant, or even 
Still others can 
suddenly rise to the top, or sink to the 
bottom like a rock, simply by adjusting 
their specific gravity. 
Some snails lay eggs: others are live- 
from the surface film. 
bearing. Some are males, some females, 
while others are normally hermaphro- 
dites, that is, possessing both male and 
female functions. One writer records 
the fact that he observed a snail exercis- 
ing the male function with a female, and 
the female function with a male at the 
same time. Still another 
recorded of two snails mutually exercis- 
ing the reproductive function. Even self- 
fertilization is said to be found among 
them. 
instance 1s 
Generally speaking, snails provided 
with an operculum are not harmful to 
plants in an aquarium. The four-horned 
snail, Ampullaria gigas, is an exception. 
A member of the Chicago Aquarium So- 
ciety recently, at our advice, dropped 
two of them into a hydra-infested tank. 
We forgot to tell him to remove them 
The result 
was that in a few days every plant in the 
(small) tank was destroyed completely. 
One of the members of the Chicago 
Aquarium Society positively declares that 
they will eat baled hay! 
when the hydra were gone. 
The writer once experimented with the 
minute wide-mouthed pond snail. They 
multiplied in the tank like the proverbial 
“chinch-bug” of Kansas. We could not 
get rid of them. The snails were very 
small, and it required patience to remove 
them. But every day we made it a part 
of the program to remove twelve snails. 
Before we had finished we had a layer a 
quarter of an inch deep, covering the bot- 
tom of a six-inch tobacco jar! 
of this snail. 
Beware 
He eats the green tissue 
out of the plants, leaving only an un- 
sightly yellow skeleton. And he’s almost 
impossible to eliminate, unless one re- 
move all the water, burn the plants, scour 
the tank and begin anew. 
For the aquarium, the beginner will 
find the Striped Potomac, Vivipara con- 
tectoides; the Jap, Vivip, malleatus,; the 
