Many other worms, a number of them un-wormlike in appearance will claim our attention but we cannot devote more space to them here. There is the common shell-binder, a curious worm, which builds for itself a still more curious shelter of broken shells. Another worm, Serpula by name, also lives in tube-like structures of its own manufacture and is remarkable in that a row of nearly two thousand seven-toothed hooks run along its back and all these thirteen thousand odd teeth are there merely for the purpose of holding Serpula in its tubular home.
Much interesting work may be done at the seaside in studying the young stages of various familiar creatures. This work, however, necessitates the keeping of the adults in an aquarium; for the young ones, in most cases, are so unlike their parents that, if found swimming about on their own account, they would never be recognised. Young barnacles, for instance, have six legs, a tubular mouth and a single eye. At a later stage they might be mistaken for young shell fish; they possess a shell, not unlike that of the mussel, containing, however, not a soft, fleshy mollusc but a six legged creature which swims through the water in jerks, after the manner of a water flea. Strangely enough, it is now provided with two stalked eyes like those of a crab, whilst of mouth parts it has none, or they are so imperfectly developed as to be useless for feeding. Soon this active youngster settles down for the rest of its life and becomes a sedate and sedentary barnacle, with one imperfectly developed eye and a mouth capable of feeding to good purpose.
Young crabs are equally curious and also totally unlike their parents, but these curious creatures are hardly accessible to those who only pay a flying visit to the sea-side. As we have remarked, an aquarium is a necessity and to keep marine animals inland is a feat beyond the powers of the ordinary mortal.
The Sea Lemon or Doris is a curious little creature, worthy of examination. Its habit is to feed upon sponges and strange diet it is, for we remember that all sponges are fortified with hard flinty structures, called spicules. This habit of the Sea Lemon is of use to the microscopist, for the stomach of the creature is always laden with the indigestible spicules and a very interesting collection of these beautiful structures may be gathered together in this manner. The egg masses of Doris may be looked for on rocks during the summer. Enormous numbers of eggs are laid in a jelly-like mass. Some of this jelly may be collected and examined under the microscope and, should we have collected our material at a favourable moment, we may watch the eggs hatch and observe the young Sea Lemons in their delicate transparent shells swimming round and round the chamber within which they are imprisoned during the very early stages of their lives.
Very frequently in the summer, when the seas are warm any agitation of the water causes a beautiful phosphorescence to appear. Phosphorescence, by the way, may be described as light without heat and it is not uncommon in nature. Glow worms and fireflies are phosphorescent; fish, also, in the dead state, often emit a certain amount of light as do bones whilst, of course, phosphorous itself is the best example of a naturally phosphorescent body. Phosphorescent sea water, however, owes its peculiarity to myriads of minute animals and they will afford us an interesting half hour with the microscope. Let us collect a little of this water in a glass jar and take it into a darkened room that we may the better see the phosphorescence. When the water in the jar is undisturbed, we can see nothing unusual; if we stir it or strike it a faint greenish light is given off, but it does not last for long. Now, on taking the jar into the daylight, as soon as our eyes are accustomed to the light, we shall just be able to see that there are some very small living creatures on the surface of the water. We must examine one, under a fairly high magnification; it may be transferred, from the jar to a drop of water on our slide, by means of a paint brush. The little animal which is responsible for the phosphorescence of sea water is strangely reminiscent of an apple with its stalk. It is, of course, very minute being only 1/60 inch in diameter and its tail, which we have compared to the stalk of the apple, is equal to the diameter in length. The whole creature is quite transparent. As we watch it swim in our drop of water, we shall notice that it propels itself by the lashing of its tail.
There are countless animals of the sea we have not so much as mentioned, but the marine gardens contain plants so interesting and so totally unlike those which live upon land that we must devote a few pages to them also.