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. [131] Hermit crab. 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. [132] Cancer Diogenes.