3. Internally there is a cavity at each end, and a passage passes through it; there is a fluid in both the cavities. Besides this, it has no sensitive or organic member, nor is there any excrementitious matter, as I said before. The colour of the tethyon is partly ochreous, partly red.
4. The class acalephe[135] is peculiar; it adheres to rocks like some of the testacea, but at times it is washed off. It is not covered with a shell, but its whole body is fleshy; it is sensitive, and seizes upon the hand that touches it, and it holds fast, like the polypus does with its tentacula, so as to make the flesh swell up. It has a central mouth, and lives upon the rock, as well as upon shell-fish, and if any small fish falls in its way, it lays hold of it as with a hand, and if any eatable thing falls in its way it devours it.
5. One species is free, and feeds upon anything it meets with, even pectens and echini; it appears to have no visible excrement, and in this respect it resembles plants. There are two kinds of acalephe, some small and more eatable, others large and hard, such as are found near Chalcis. During winter their flesh is compact, wherefore in this season they are caught and eaten; in summer time they perish, for they become soft; if they are touched they soon melt down, and cannot by any means be taken away. When suffering from heat, they prefer getting under stones. I have now treated of malacia, malacostraca, testacea, and of their external and internal parts.
Chapter VII.
1. Insects must now be treated of in the same manner. This is a class which contains many forms, and no common name has been given to unite those that are naturally related, as the bee, anthrene,[136] and wasp, and such like; again, those which have their wings enclosed in a case, as the melolontha,[137] carabus,[138] cantharis, and such like. The common parts of all insects are three—the head, the abdomen, and the third, which is between these, such as in other animals is the breast and back. In many insects this is one, but in the long insects with many legs, the middle parts are equal to the number of segments.
2. All insects survive being divided, except those which are naturally cold, or soon become so from their small size, so that wasps live after they are cut asunder; either the head or the abdomen will live if united to the thorax, but the head will not live alone. Those which are long, and have many feet, will survive division for a considerable time; both the extremities are capable of motion, for they walk both upon the part cut off and upon the tail, as that which is called scolopendra. All of them have eyes, but no other manifest organs of sense, except that some have a tongue. All the testacea have this organ, which serves the double purpose of tasting and drawing food into the mouth.
3. In some of them this organ is soft; in others very strong, as in the purpura; in the myops and œstrus this member is strong, and in a great many more; for this member is used as a weapon by all those that have no caudal sting.
4. Those with this weapon have no small external teeth, for flies draw blood by touching with this organ, and gnats sting with it. Some insects also have stings, which are either internal, as in bees and wasps, or external, as in the scorpion. This last is the only insect that has a long tail; it has claws, and so has the little scorpion-like creature[139] found in books. The winged insects, in addition to other parts, have wings. Some have two wings, as the flies; others four, as the bees; none of the diptera have a caudal sting. Some of the winged insects have elytra on their wings, as the melolontha; and others no elytra, as the bee. Insects do not direct their flight with their tail, and their wings have neither shaft nor division.
5. Some have a horn before their eyes, as the psychæ[140] and carabi. Of the jumping insects, some have their hind-legs larger; others have the organs of jumping bent backwards, like the legs of quadrupeds. In all, the upper part is different from the lower, like other animals.
6. The flesh of their bodies is neither testaceous nor like the internal parts of testacea, but between the two. Wherefore, also, they have neither spine nor bone, as the sepia; nor are they surrounded with a shell. For the body is its own protection by its hardness, and requires no other support; and they have a very thin skin. This is the nature of their external parts.