1, Animal with tentacles t, bearing small tendrils t´. 2, Body of animal enlarged. m, Mouth. c, Digestive cavity. s, Sac into which the tentacles are withdrawn. p, Bands with comb-like plates. 3, Portion of a band enlarged to show the moving plates p.
Let us take the Cydippe first (1, Fig. 71). I have six here, each in a separate tumbler, and could have brought many more, for when I dipped my net in the pool yesterday such numbers were caught in it that I believe the retreating tide must just have left a shoal behind. Put a tumbler on the desk in front of you, and if the light falls well upon it you will see a transparent ball about the size of a large pea marked with eight bright bands, which begin at the lower end of the ball and reach nearly to the top, dividing the outside into sections like the ribs of a melon. The creature is so perfectly transparent that you can count all the eight bands.
At the top of the ball is a slight bulge which is the mouth (m 2, Fig. 71), and from it, inside the ball, hangs a long bag or stomach, which opens below into a cavity c, from which two canals branch out, one on each side, and these divide again into four canals which go one into each of the tubes running down the bands. From this cavity the food, which is digested in the stomach, is carried by the canals all over the body. The smaller tubes which branch out of these canals cannot be seen clearly without a very strong lens, and the only other parts you can discern in this transparent ball are two long sacs on each side of the lower end. These are the tentacle sacs, in which are coiled up the tentacles, which we shall describe presently. Lastly, you can notice that the bands outside the globe are broader in the middle than at the ends, and are striped across by a number of ridges.
In moving the tumblers the water has naturally been shaken, and the creature being alarmed will probably at first remain motionless. But very soon it will begin to play in the water, rising and falling, and swimming gracefully from side to side. Now you will notice a curious effect, for the bands will glitter and become tinged with prismatic colours, till, as it moves more and more rapidly these colours, reflected in the jelly, seem to tinge the whole ball with colours like those on a soap-bubble, while from the two sacs below come forth two long transparent threads like spun glass. At first these appear to be simple threads, but as they gradually open out to about four or five inches, smaller threads uncoil on each side of the line till there are about fifty on each line. These short tendrils are never still for long; as the main threads wave to and fro, some of the shorter ones coil up and hang like tiny beads, then these uncoil and others roll up, so that these graceful floating lines are never two seconds alike.
We do not really know their use. Sometimes the creature anchors itself by them, rising and falling as they stretch out or coil up; but more often they float idly behind it in the water. At first you would perhaps think that they served to drive the ball through the water, but this is done by a special apparatus. The cross ridges which we noticed on the bands are really flat comb-like plates (p, Fig. 71), of which there are about twenty or thirty on each band; and these vibrate very rapidly, so that two hundred or more paddles drive the tiny ball through the water. This is the cause of the prismatic colours; for iridescent tints are produced by the play of light upon the glittering plates, as they incessantly change their angle. Sometimes they move all at once, sometimes only a few at a time, and it is evident the creature controls them at will.
This lovely fairy-like globe, with its long floating tentacles and rainbow tints, was for a long time classed with the jelly-fish; but it really is most nearly related to sea-anemones, as it has a true central cavity which acts as a stomach, and many other points in common with the Actinozoa. We cannot help wondering, as the little being glides hither and thither, whether it can see where it is going. It has nerves of a low kind which start from a little dark spot (ng), exactly at the south pole of the ball, and at that point a sense-organ of some kind exists, but what impression the creature gains from it of the world outside we cannot tell.
I am afraid you may think it dull to turn from such a beautiful being as this, to the grey leaf which looks only like a dead dry seaweed; yet you will be wrong, for a more wonderful history attaches to this crumpled dead-looking leaf than to the lovely jelly-globe.
First of all I will pass round pieces of the dry leaf (r, Fig. 72), and while you are getting them I will tell you where I found the living ones. Great masses of the Flustra, as it is called, line the bottom and sides of my pool. They grow in tufts, standing upright on the rock, and looking exactly like hard grey seaweeds, while there is nothing to lead you to suspect that they are anything else. Yesterday I chipped off very carefully a piece of rock with a tuft upon it, and have kept it since in a glass globe by itself with sea-water, for the little creatures living in this marine city require a very good supply of healthy water and air. I have called it a "marine city," and now I will tell you why. Take the piece in your hand and run your finger gently up and down it; you will glide quite comfortably from the lower to the higher part of the leaf, but when you come back you will feel your finger catch slightly on a rough surface. Your pocket lens will show why this is, for if you look through it at the surface of the leaf you will see it is not smooth, but composed of hundreds of tiny alcoves with arched tops; and on each side of these tops stand two short blunt spines (see 2, Fig. 72), making four in all, pointing upwards, so as partly to cover the alcove above. As your finger went up it glided over the spines, but on coming back it met their points. This is all you can see in the dead specimen; I must show you the rest by diagrams, and by and by under the microscope.
Fig. 72.
