Chapter IV.

1. The testacea, as cochleæ,[120] and cochli,[121] and all that are called ostrea,[122] and the family of echini, are composed of flesh, and this flesh is like that of the malacostraci, for it is internal; but the shell is external, and they have no hard internal part. But they have many differences amongst themselves, both in regard to their external shells and their internal flesh, for some of them have no flesh at all, as the echinus; in others it is entirely internal and out of sight, except the head, as the land snails and those called coccalia,[123] and in the sea the purpura[124] and the ceryx,[125] the cochlus, and all the turbinated shells.

2. Of the rest some are bivalves, others univalves. I call those bivalves which are enclosed in two shells; the univalves are enclosed in one shell, and the fleshy part is uncovered, as the lepas.[126] Some of the bivalves can open, as the pectens and mya, for all these are joined on one side, and separated on the other, so as to shut and open. There are other bivalves which are joined on both sides, as the solen; others which are entirely enclosed in their shells, and have no external naked flesh, as those which are called tethya.[127]

3. And there is a great difference amongst the shells themselves, for some are smooth, as the solen, mya, and some conchæ, called by some persons galaces;[128] other shells are rough, as the limnostrea,[129] pinnæ, some kinds of conchæ, and the whelk; and of these some are marked with ridges, as the pecten and a kind of concha, others are without ridges, as the pinna and another species of concha. They also differ in thickness and thinness, both in the whole shell and in certain parts of the shell, as about the edges, for in some the edges are thin, as the mya; others are thick-edged, as the limnostrea.

4. Some of them are capable of motion, as the pecten, for some persons say that the pectens can fly, for that they sometimes leap out of the instrument by which they are taken. Others, as the pinna, cannot move from the point of attachment; all the turbinated shells can move and crawl; the lepas (patella) also feeds by going from place to place. It is common to all those with hard shells to have them smooth in the inside.

5. Both in univalves and bivalves the fleshy part is united to the shell, so that it can only be separated by force; it is more easily separated from the turbinated shells; it is a characteristic of all these shells, that the base of the shell has the helix directed from the head. All of them from their birth have an operculum; all the turbinated testacea are right-handed, and move, not in the direction of the helix, but the contrary way.

6. The external parts of these creatures are thus distinguished; the nature of their internal structure is similar in all, especially in the turbinated animals, for they differ in size and in the relations of excess, the univalves and bivalves do not exhibit many differences. Most of them have but few distinctive marks from each other, but they differ more from the immovable creatures. This will be more evident from the following considerations. In nature they are all alike, the difference, as before said, is in excess; for in larger species the parts are more conspicuous, and less so in those that are smaller. They differ also in hardness and softness, and such like affections.

7. For all have on the outside of the shell, in the mouth, a hard piece of flesh, some more, some less; from the middle of this are the head and the two horns; these are large in larger species, in the little ones they are very small. The head is protruded in the same manner in all of them, and when the creature is alarmed it is again retracted; some have a mouth and teeth, as the snail, which has small, sharp, and smooth teeth.

8. They have also a proboscis, like that of the fly, and this organ is like a tongue. In the ceryx and the purpura this organ is hard, like that of the myops and œstrus, with which they pierce through the skins of quadrupeds; but this is more powerful in strength, for they can pierce through the shells of the baits. The stomach is joined quite closely to the mouth; the stomach of the cochlus is like the crop of a bird; below this there are two hard white substances like nipples, which also exist in the sepia, but are much harder.

9. From the stomach a long, simple intestine reaches as far as the spiral, which is on the extremity of the body. These are distinct, and in the purpura and the ceryx are in the helix of the shell. The bowel is continuous with the intestine. The intestine and bowels are joined together, and are quite simple, to the anus. The origin of the bowel is around the helix of the mecon,[130] and here it is wider. The mecon is, as it were, a superfluous part in all testacea, afterwards another bend causes it to return to the fleshy part; the end of the entrail, where the fæces are emitted, is near the head, and is alike in all turbinated shells, whether terrestrial or marine.

10. In the larger cochli a long white passage, contained in a membrane, and in colour resembling the upper mastoid appendages, is joined from the stomach to the œsophagus, and it is divided into segments like the ovum of the carabus, except that it is white, while the other is red. It has neither exit nor passage, but it is contained in a thin membrane, which has a narrow cavity. From the intestine black and rough bodies descend continuously, like those in the tortoise, but they are less black.

11. Both these and white bodies occur in the marine cochli, but they are less in the smaller kinds. The univalves and bivalves are in some respects like these, and in others they are different, for they have a head, horns, and mouth, and something like a tongue, though in smaller species these are inconspicuous from their minute size, and they are not discernible when the animals are dead or at rest. They all contain the mecon, but not in the same position, nor of the same size, nor equally conspicuous. In the lepas it is in the bottom of the shell, in the bivalves near the hinge.

12. They all have hair-like appendages placed in a circle, and so have the pectens, and that which is called the ovarium in those that have it; where it is possessed, it is placed in a circle on the other side of the circumference, like the white portion in the cochli, for this is alike in all. All these parts, as I have said, are conspicuous in the larger kinds, but in smaller not at all, or scarcely so, wherefore they are most conspicuous in the larger pectens, and these have one valve flat like an operculum.

13. The anus is placed in the side in some of these creatures, for this is where the excrement passes out. The mecon, as I have said, is a superfluous part enclosed in a thin membrane in all of them; that which is called the ovarium has no passage in any of them, but it swells out in the flesh. This is not placed upon the intestine, for the ovarium is on the right side and the intestine on the left; the anus is the same as in others; but in the wild patella, as some persons call it, or the sea-ear (haliotis), as it is named by others, the excrement passes out below the shell, for the shell is perforated. The stomach also is distinct behind the mouth, and so is the ovarium in this animal. The position of all these parts may be seen in dissections.

14. The creature called carcinium[131] resembles both the malacostraca and the testacea, for this in its nature is similar to the animals that are like carabi, and it is born naked (not covered with a shell). But because it makes its way into a shell, and lives in it, it resembles the testacea, and for these reasons it partakes of the character of both classes. Its shape, to speak plainly, is that of a spider, except that the lower part of the head and thorax is larger.

15. It has two thin red horns, and two large eyes below these, not within nor turned on one side, like those of the crab, but straight forwards. Below these is the mouth, and round it many hair-like appendages; next to these, two divided feet with which it seizes its prey, and two besides these on each side, and a third pair smaller. Below the thorax the whole creature is soft, and when laid open is yellow within.

16. From the mouth is a passage as far as the stomach; but the anus is indistinct; the feet and the thorax are hard, but less so than those of the cancri; it is not united with the shell like the purpura and ceryx, but is easily liberated from it. The individuals which inhabit the shells of the strombus are longer than those in the shells of the nerita.

17. The kind which inhabits the nerita is different, though very like in other respects, for the right divided foot is small, and the left one large, and it walks more upon this than the other; and a similar animal is found in the conchæ, though they are united to their shells very firmly; this animal is called cyllarus.[132] The nerita has a smooth, large, round shell, in form resembling that of the ceryx, but the mecon is not black, but red; it is strongly united in the middle.

18. In fine weather they seek their food at liberty, and if a storm arises, the carcinia hide themselves under a stone, and the neritæ attach themselves to it like the patella, the hæmorrhois, and all that class, for they become attached to the rock, where they close their operculum, for this resembles a lid; for that part which is in both sides in the bivalves is joined to one side in the turbinated shells: the interior is fleshy, and in this the mouth is placed.

19. The nature of the hæmorrhois, the purpura, and all such animals is the same. But those which have the left foot greater are not found in the shells of the strombus, but in the neritæ. There are some cochli which contain an animal like the small astacus, which is found in rivers; but they differ from them in having the inner part of the shell soft. Their form may be seen by examining dissections.