THE YOUNG SCIENTIST. 
5 
Marvels of Pond Life— Y. 
ALTHOUGH the polyps are remarkable 
for the simplicity of their organization, 
they do not the less exhib' the wonderful 
nature of animal life, laeir bodies are 
composed of the substance, ca.lledsarcode, 
in which is imbedded a coloring matter 
resembling that in the leaves of plants ; 
every part possesses irritability and con- 
tractility, and they are very sensitive to 
the stimulus of light. The outer layer of 
their bodies is harder than the inner layer. 
These layers are severally called ectoderm 
and endoderni. They may be cut and 
grafted like trees, and if turned inside out, 
the new inside digests and assimilates as 
well as the old. Whether any form of 
consciousness can belong to creatures 
which have no distin ct nervous system is 
open to doubt, but it would seem probable 
from their movemeats that food and light 
afford them something like a pleasurable 
sensation iu a very humble degree. If we 
were sufficiently acquainted with the 
secrets of molecular combination we might 
discover that the various functions of 
these simple organisms were discharged 
by different par^ic^es, although it is only 
in higher creatures that muscular particles 
are aggregated into muscles, or nerve 
particles into nerves. 
Having examined the general appear- 
ance and proceedings of the hydra, let us 
cut off a tentacle, or take a small specimen 
and gently crush it by pressing down the 
cover of the live box, and place the object 
so prepared under a power of about three 
hundred linear. If we then illuminate it 
with a moderate quantity of oblique light, 
we shall discover round the edge of the 
tentacle a number of small cells or cap- 
sules, from some of which a very slender 
wire or thread will be emitted.* These 
are the stinging organs of the polyp, and 
resemble those wtiich Mr. Gosse has so 
ably elucidated in the sea anemones. 
Some writers have endeavored to show 
that they are not stinging organs at all, 
but so large an amount of evidence to the 
contrary is accumulated in Mr. Gosse 's 
* Actinologia Britannica,' that no reason- 
able doubt remains. The stinging cap- 
sules of the polyp are shown in the an- 
nexed sketch, and also the way in which 
they are employed, for it fortunately 
happened that on exposing one of the 
hydras to pressure in the live box, a small 
worm (AnguiUula) escaped, which had 
been pierced with the minute weapons 
which are supposed to convey a poison 
into the wound. The authors of the 
' Mi orographic Dictionary ' think that the 
prongs of the forks, which will be seen to 
* See c and d, page 150, Dec, 1881. 
point upwards in the sketch,* are springs, 
and occupy a reversed position in the 
capsule cells, and that their function is to 
throw out the threads. However this may 
Anguilhila pierced by stinging organs of the 
Hydra mridis. X 300. 
be, the polyps, and similarly endowed 
creatures, have the power of darting out 
their poison threads with considerable 
force, and Mr. Gosse found that the 
anemone was able to pierce a thick piece 
of human skin. 
The same excellent observer attributes 
the emission of the anemone poison 
threads, which he considers hollow, to the 
injection of a fluid. In their quiescent 
state, he thinks they are drawn in, like 
the finger of a glove, and are forced out 
as the liquid enters their slender tubes. 
Possibly the polyp stinging organs may 
have the same structure. 
Notwithstanding their dangerous wea- 
pons, polyps are often infested with a 
