Fig. 18.
The Marsh-snail
(Lymnea communis).
“It is different in shape, but it is nearly allied in other respects, for that is the Marsh-snail, or Lymnea. Some of the species of this genus crawl with their backs downwards along the under surface of the water, if I may so describe it, just as you have seen a snail crawl on a glass; and the species of the genus Physa, which is another little black fresh-water-snail, not only creep in the manner I have described, but let themselves down by a thread in the water, just as you may have seen some kinds of caterpillars do on land.”
As they strolled along the beach they noticed several immense plants of Sea-rocket, which grew close to the cliffs, and some of the fleshy leaves of which Agnes gathered and ate. “I know I am safe in eating this,” said she; “because I see by the four opposite petals of the flower that it is one of the Cruciferæ, or cabbage-tribe, and I know the plants of that tribe are wholesome.”
“Take care, however, lest you should some day find that though the Cruciferous plants are eatable they are not always agreeable; for, remember, Horseradish, and some other pungent plants, belong to that tribe: but I am glad to find that you have remembered what I told you about the shape of the flowers, which are called cruciferous, or cross-bearing, from their four petals being arranged in the form of a Greek cross.”
Agnes now found a specimen of the Star-fish, or five-fingers, a species of which she had often seen in Scotland; but she did not attempt to pick it up, as she remembered that one she found at Dunbar began to decay before she could reach the inn. She stood, however, looking at it, and her mother, who told her these Star-fishes were usually only caught in the Northern seas, made her remark its mouth, or rather the opening to its short bag-like stomach, which is placed in the very centre of the rays; and the numerous holes through which the creature could project its feet, having the power of shortening or extending them at pleasure, and also of adhering, by the flat disk at their base, to any substance it might be near; the part which may be called the sole of the foot, acting like a sucker.
Fig. 19.
The Star-fish, or Five-fingers (Asterias glacialis).
“What poor helpless creatures these Star-fish seem to be!” said Agnes; “I wonder how they contrive to live, for they seem to have no means of catching anything.”
“You will be surprised, then, to hear that they are accused of catching oysters; and that it is asserted in many books on natural history, that there was formerly a penalty inflicted by the Admiralty Court on every dredger who caught a Star-fish and did not kill it.”