“Ah, mamma!” said Agnes, “then these creatures are polypes. I have been frequently going to ask you what kind of creatures they were, ever since papa was reading to us that curious account of the manner in which they form islands in the Australian Seas. But surely,” continued she, after thinking for a moment, “these soft jelly-like looking animals cannot possibly form any thing so hard as coral!”
“It is, indeed,” replied Mrs. Merton, “extremely difficult for us to conceive that animals so simple and jelly-like can form solid stone; but the way in which it is effected is, that the creature has the power of depositing, in a solid form, the earthy matter which is continually floating in the waters of the ocean, and which it swallows with its daily food.”
While Agnes and her mamma were thus speaking they continued descending the cliffs till they came to the part where the road turns, and leaves a little level space before it again descends. Just at this place they found an old woman sitting at a kind of stall covered with shells and various kinds of fossils; and Agnes, whose curiosity was always easily excited, stopped to look at them.
“I wish we could find any polypes here,” said she to her mamma.
“It is impossible,” said Mrs. Merton, “to find any here in a living state; but you may see some of their labours in these curious specimens of sponge.”
“Sponge, mamma?” cried Agnes. “Surely you do not mean to say that the polypes form sponge as well as coral!”
Fig. 24.
Sponges.
“Indeed I do,” said Mrs. Merton, “for though sponge was once supposed to be a marine plant, it has long since been discovered to be an animal. About the year 1752 a gentleman, named Ellis, was at Brighton forming a collection of marine plants for the instruction of some part of the Royal Family in botany, and amongst other things he collected some curious specimens of sponges, which he examined through a powerful microscope with a view to obtain a knowledge of some peculiarities which he considered necessary to be ascertained before they could be properly classified. By this examination he discovered that the sponges possessed a system of vessels through which the sea-water circulated, and which opened by means of innumerable pores. Subsequent examinations proved that what we call sponge may be compared to the shell of the snail or the oyster, and that it acts as a covering to the jelly-like animal or animals which reside in it, being as necessary to them as shells are to the molluscous animals. Mr. Ellis, after making these discoveries, examined different kinds of coral, and found that they were also furnished with pores containing animals, the tentacula or feelers of which were continually expanding and contracting as if seeking and seizing prey.”
“How very curious!” cried Agnes; “and what do these creatures live upon?”