HYDRA. 
fore, means to pass from the sides of the 
glass to the surface of the water, it has 
only to put that part out of the water by 
which it is to be supported, and to give it 
time to dry, which it always does upon 
these occasions ; and they attach them- 
selves so firmly by the tail to aquatic plants, 
stones, &c. that they cannot be easily dis- 
engaged: they often further strengthen 
these attachments by means of one or two 
of their arms, which serve as a kind of 
anchors for fixing them to the adjacent 
substances. 
The fusca has the longest arms, and 
makes use of the most curious manoeuvres 
to seize its prey. They are best viewed 
in a glass seven or eight inches deep, 
when their arms commonly hang down to 
the bottom. When this or any other kind 
is hungry, it spreads its arms in a kind of 
circle to a considerable extent, inclosing 
in this, as in a net, every insect which has 
the misfortune to come within the circum- 
ference. While the animal is contracted 
by seizing its prey, the arms are observed 
to swell like the muscles of the human body 
when in action. Though no appearance 
of eyes can be observed in the polype, they 
certainly have some knowledge of the ap- 
proach of their prey, and show the greatest 
attention to it as soon as it comes near 
them. It seizes a worm the moment it is 
touched by one of the arms; and in con- 
veying it to the mouth, it frequently twists 
the arm into a spiral like a cork-screw, by 
which means the insect is brought to the 
mouth in a much shorter time than other- 
wise it w'ould be ; and so soon are the in- 
sects on which the polypes feed killed by 
them, that M. Fontana thinks they must 
contain the most powerful kind of poison ; 
for the lips scarcely touch the animal when 
it expires, though there cannot be any 
wound perceived on it when dead. The 
worm, when swallowed, appears sometimes 
single, sometimes double, according to cir- 
cumstances. When full, the polype con- 
tracts itself, hangs down as in a kind of 
stupor, but extends again in proportion as 
the food is digested, and the excrementi- 
tious part is discharged. The manner in 
which the polypes generate is most per- 
ceptible in the grisca and fusca, as being 
considerably larger than the viridis. If we 
examine one of them in summer, when the 
animals are most active, and prepared for 
propagation, some small tubercles will be 
found proceeding from its sides, which con- 
stantly increase in bulk, until at last in two 
or three days they assume the figure of 
small polypes. When they first begin to 
shoot, the excrescence becomes pointed, 
assuming a conical figure, and deeper colour 
than the rest of the body. In a short time 
it becomes truncated, and then cylindrical, 
after which the arms begin to shoot from 
the anterior end. The tail adheres to the 
body of the parent animal, but gradually 
grows smaller, until at last it adheres ouly 
by a point, and is then ready to be sepa- 
rated. When this is the case, both the 
mqther and young ones fix themselves to 
the sides of the glass, and are separated 
from each other by a sudden jerk. The 
time requisite for the formation of the 
young ones is very different, according to 
the warmth of the weather, and the nature 
of the food eaten by the mother. Some- 
times they are fully formed, and ready to 
drop off in twenty-four hours ; in other 
cases, when the weather Is cold, fifteen 
days have been requisite for bringing them 
to perfection. The polypes produce young 
ones indiscriminately from all parts of their 
bodies, and five or six young ones have fre- 
quently been produced at once; nay, M. 
Trembley has observed nine or ten pro- 
duced at the same time. Nothing like 
copulation among these creatures was ever 
observed by M. Trembley, though for two 
years he had thousands of them under his 
inspection. 
When a polype is cut transversely, or 
longitudinally, into two or three parts, each 
part in a short time becomes a perfect ani- 
mal; and so great is this prolific power, 
that a new animal will be produced even 
from a small portion of the skin of the old 
one. If the young ones be mutilated 
while they grow upon the parent, the parts 
so cut off will be reproduced; and the 
same property belongs to the parent. A 
truncated portion will send forth young 
ones before it has acquired a new head 
and tail of its awn, and sometimes the head 
of the young one supplies the place of that 
which should have grown out of the old 
one. If we slit a polype longitudinally 
through the head to the middle of the body, 
we shall have one formed with two heads ; 
and by again slitting these in the same 
manner, we may form one with as many 
heads as we please. A still more sur- 
prizing property of these animals is, that 
they' may be grafted together. If the 
truncated portions of a polype be placed 
end to end, and gently pushed together, 
they will unite into a single one. The two 
