Buchanan County bulletin. [volume] (Independence, Iowa) 1869-1891, 1878-11-01
EDUCATIONAL DEPARTMENT,
POND BIOLOGY.
BY PROF. SAMUEL CALVIN,
VIM. ELDEN, Editor.

TO the teacher who loves to pry into
the secret ways of Nature, who is curl
Gus to know how the myriads Of Gods
creatures live and move and breathe,
and who would delight to lead his pupils
in ways of knowledge as far removed as
possible from methods that have proved
so effectual in the artificial production
OF stupidity, a microscope which need
cost no more than ten dollars, and a
convenient pond which need cost moth
ing at all, will be found to be infinite
sources of pleasure and instruction.
A few common wigglers are easily
collected, and one of these with just
water enough to cover it. may be placed
on the glass slide of the microscope.
Putting the little fellow under proper
restraint, we may, with power Of less
than a hundred diameters, make out the
whole internal structure. Attend first
to two dark lines that run the whole
length Of the body. Following them
backward we find they have common
starting point in one branch of the fork
ed tail. We may notice now that the
free specimens left in the water are
nearly all hanging, head downward, with
this particular branch of the tail
brought to the surface These lines
must be connected with structures Of
some importance to our little wiggler.
A little pressure upon the specimen we
are examining and bubble Of air ap-
tangled in minute whorls Of bristles
relieve the pressure and the bubble is at
once absorbed. The dark lines are air
tubes; are the wiggler's breathing Or
gans, and it needs only little examina-
ton to see that they are only the main
trunks of a complex system OF tubes
running throughout the body and carry
ing air to every part of it.
What kind of tubes are they? If the
walls be soft and thin they will collapse
and so shut out the air, or, at least, they
will be closed in places by the wriggling
movements Of the animal and therefore
work imperfectly. They cannot be stiff
and igid, for then they would interfere
with the wonderful fexibility the crea-
ture displays Here then is problem.
How can system of tubes be con-
structed so as to be always open and yet
have the walls light and thin and per-
fectly flexible? These difficult condi-
tions are met, as any one may see with
a little trouble, by one of the most ad
mirable contrivances to be found in the
whole range of organic adaptation. The
air tubes are double; each consists of
tube within tube with walls of ex-
treme delicacy. Between the outer and
inner wall there is wound spirally mi
mute thread having sufficient elasticity
to keep the tube always open without
in the least interfering with its perfect
fexibility With even our low power
instrument we may see this little spiral
in some parts of the tubes, particularly
near their origin. By carefully dissect-
ing a larger insect the spiral thread may
be taken out and removed.
/ Looking next between the two breath
ing tubes, just behind the middle of the
body we see the rhythmic pulsations Of
the heart This organ is also simple
tube, and extends nearly the whole
length of the back. With every beat we
see the blood forced headwards Why
should it go in that direction rather
than in the other? We can see for our
selves. Carefully adjusting the instru-
ment and looking steadily for moment
or two. we discover a system of valves.
Psll ioI SdSh JolIl. opOhiHS "hNa
closing with the utmost regularity.
They can open in only one way, and
when the walls of the heart contract
they effectually prevent any backward
flow, without, however, offering any OBJ
stacle to movement of the fluid in the
opposite direction At the anterior end
of the heart the blood is poured into
channels excavated in and amongst the
tissues, and finds its way back with
wonderful rapidity to the posterior part
of the body whence it is again pumped
forward through that simple but effect
i've heart
Next, the alimentary canal may be
observed throughout its entire length.
Little pellets of food passing from the
mouth along the esophagus, plainly Wis
ible; the digestion Of food in the stom
ach or stomachs, and the peristaltic
movements of the intestincs are easily
seen. Eyes and jaws and glands and
nerve centers may be made out. 1t only
requires little patience, little prac-
tice in observation, little sharpening
of the intellectual vision to see and ap-
preciate the working of the whole Won
derful mechanism.