Chapter V.
1. The echini contain no flesh, but this part is peculiar, for they are all of them void of flesh, and are filled with a black substance. There are many kinds of echinus, one of which is eatable; in this one the ova are large and eatable, both in the greater and the less.
2. And there are two other kinds, the spatangus and that called bryttus; these are inhabitants of the sea, and rare. Those which are called echinometræ[133] are the largest of all. Besides this, there is another small species, which has long and sharp spines; this is procured from the sea, in many fathoms water, and some persons use it for stranguary.
3. Around Torona there are white marine echini, which have shells, and prickles, and ova, and are longer than others; but the prickle is neither large nor strong, but soft, and the black parts from the mouth are more in number, and united to the outward passage, but distinct among themselves, and by these the animal is as it were divided. The eatable kinds are particularly and especially active, and it is a sign of them; for they have always something adhering to their spines.
4. They all contain ova, but in some they are very small, and not eatable: that which is called the head and mouth in the echinus is downwards, and the anus placed upwards. The same thing occurs in the turbinated shells, and the patella; for their food is placed below them, so that the mouth is towards the food, and the anus at or on the upper part of the shell.
5. The echinus has five hollow internal teeth, in the midst of these a portion of flesh like a tongue; next to this is the œsophagus; then the stomach, in five divisions, full of fæculent matter: all its cavities unite in one, near the anus, where the shell is perforated. Beneath the stomach, in another membrane, are the ova, the same number in all, they are five in number, and uneven.
6. The black substance is joined above to the origin of the teeth, this black substance is bitter and not eatable; in many animals there is either this substance or its analogue, for it is found in tortoises, toads, frogs, turbinated shells, and in the malacia; these parts differ in colour, but are entirely or nearly uneatable. The body of the echinus is undivided from beginning to end, but the shell is not so when seen through, for it is like a lantern, with no skin around it. The echinus uses its spines as feet, for it moves along by leaning upon them and moving them.
Chapter VI.
1. The creatures called tethya[134] have a most distinct character, for in these alone is the whole body concealed in a shell. Their shell is intermediate between skin and shell, so that it can be cut like hard leather: this shell-like substance is attached to rocks; in it there are two perforations, quite distant from each other, and not easily seen, by which it excludes and receives water, for it has no visible excrement as other testacea, neither like the echinus, nor the substance called mecon.
2. When laid open, there is first of all a sinewy membrane lining the shell-like substance, within this the fleshy substance of the tethyon. Unlike any other creature, its flesh, however, is alike throughout, and it is united in two places to the membrane and the skin from the side, and at its points of union it is narrower on each side; by these places it reaches to the external perforations which pass through the shell; there it both parts with and receives food and moisture, as if one were the mouth, the other the anus, the one is thick, the other thinner.