the observer and the animal (not directly but obliquely, so as to make the angle of reflection more or less acute), the reflections will take yellow, orange, scarlet and crimson hues.
As it crawls, the Aphrodite usually elevates the tail, which is so folded together as to form a deep groove beneath. By watching this we see now and then ejected a stream of water, with considerable force. I found that the jet occurred once in twenty five seconds, with punctual regularity. This is a respiratory act; the grooved orifice through which the jet is poured is not the termination of the intestine, as we may at first suppose, but the exit of a capacious chamber which is external to the body, though concealed.
A very marvellous and quite unparallelled structure here comes into view. If we take a Sea-mouse into our hand, we see the whole breadth of the back occupied by a woolly substance, closely resembling felt, and formed by the interlacing of fine hairs. If we insert a pen-knife into the tail-groove and slit up this felt-like cover, we expose an ample cavity running the whole length of the animal, the floor of which is the true skin of the back, on which are set two rows of large overlapping plates, or membranous scales (elytra).
The dense tissue of interwoven hair resembling felt acts as a filter for the water to be respired, straining off the earthy particles held in it, which thus accumulate in its substance, and impart that peculiar dirty appearance which it possesses. The scales, according to Dr. Williams,[1] are periodically elevated and de-
- ↑ Report on the British Annellida, 200.
