The adult crinoid of the Silurian was very like the larval comatula of the present age.[37] The comatula is attached to a stalk that grows upon a rock or some other fixed substance, but at the age of six months the comatula detaches itself from this stalk and swims off. In this it differs from the barnacle which, as you may remember, is free and vagrant as a larva, and attached when adult. The crinoids of the Silurian were always fastened and grew each in its individual place, as firmly as the lilies from which they take their name. The stem of our crinoid as it is laid bare in the rock, exhibits a series of little disks or plates. These are set one above the other to form the stem, which is often several feet long. Through all these little plates there ran a soft solid substance, like an elastic cord. As the stone which holds the fossil is laid open by our chisel, and the crinoid stem and flower-cup are well displayed, they remind us of the spinal column and brain of vertebrate animals. The great German scholar and poet, Goethe, remarked that the spinal marrow threaded through the closely united vertebræ enters the skull by an opening at its base, and expands, or blooms out, into the brain. Goethe considered this a growth like a lily; the spinal cord being the stem, and the brain the perfect flower. This white stone lily looks like a prophecy in stone of the spinal cord and its brain expansion. When this crinoid was alive, these valves or petals, which now in the petrified specimen form a solid cup, were capable of opening or unfolding, and from them the long feathery filaments spread forth. Following our crinoid down the ages have come all the marvellous families of the radiates. It has become a common form of speech to call nearly every animal that lives in the sea, a fish. Thus we speak of star-fish, meaning members of the radiate family which have nothing in common with true fishes, except the habit of living in water; we call mollusks shell-fish, but they are very far removed in structure from the fish-class; also we call whales, dugongs, and their kin, fish, when instead they belong to the mammals, as we shall find when we come to study them. These star-fish, as we wrongly call them, belong to the same class as their ancient forerunners the crinoids, and the crinoids were living with the corals long before there were any fish in the ancient world. The Silurian period was almost at its close[38] before a single fish appeared in the swarming life of the ancient ocean.