118 THE OCEAN WORLD. 
system, heart, muscular rings, lungs, nor liver; the organs of the 
senses—namely, those of sight, hearing, and of smell—have also 
been denied them. Nevertheless, they act as if they possessed all 
these senses. O Nature! how hidden are thy secrets, and how the 
pride of man is humbled by the mysteries which surround thee—by 
the spectacles which strike his eye, and which he attempts in vain 
to explain ! 
Trembley states that the fresh-water polyps, having no muscular 
system, can neither extend nor contract themselves, nor can they 
progress. If touched, or if the water in which they are immersed is 
suddenly agitated, they are certainly observed to contract more or 
less forcibly, and even to inflect themselves in all directions ; and by 
this power of extension, of contraction, and inflection, they contrive 
to move from place to place; but these movements are singularly 
slow, the utmost space they have been observed to traverse being 
about eight inches in the twenty-four hours. 
Painfully conscious of his powers of progression, however, he 
has found means of remedying it, and the freshwater snail is 
his steed ; he creeps upon the shell of a Planorbis, or a Limneus, 
and by means of this improvised mount he will make more 
way in a few minutes than he would in a whole day by his own 
unassisted efforts. 
Hydra viridis, although destitute of organs of sight, is neverthe- 
less sensible of light; if the vase containing them is placed partly in 
shade and partly in the sun, they direct themselves immediately 
towards the hght ; they appreciate sounds ; they attach themselves to 
aquatic plants and other floating bodies. Without eyes, without 
brain, and without nerves, these animals lie in wait for their prey, 
recognise, seize, and devour it. They make no blunder, and only 
attack where they are pretty sure of success. They know how 
to flee from danger ; they evade obstacles, and fight with or fly 
before their enemies. There are, then, some powers of reflec- 
tion, deliberation, and premeditated action in these insignificant 
creatures ; their history, in short, is calculated to fill the mind with 
astonishment. 
Trembley insists much upon the address which the Hydra employs 
to secure its prey: by the aid of its long arms, small animals, which 
serve to nourish it, are seized, for it is carnivorous, and even passably 
voracious. Worms, small insects, and larva of dipterous insects are 
its habitual prey. When a’ worm or water flea in passing’ its tentacles 
happens to touch them, the polyp, taking the hint, seizes upon the 
wanderer, twining its flexible arms round it, and, directing it rapidly 
