3500. In the following families the body is free and sacciform, provided with arms or fins, and mostly with eyes upon a kind of head.
These animals have the mouth situated above or in front of the body, and are distinctly separated into mantle and abdomen, while they are frequently surrounded by a shell. They have a kind of head with tentacles or arms, and frequently furnished with eyes like the Snails, or pretty nearly like the Fishes; the sexual parts united and separated. They all row, paddle, or steer themselves about in the sea.
Fam. 5. Snail-Kracken—Pteropoda.
Body mostly gelatinous, sacciform, closed all round and free; fins upon the sides of the neck, with two tentacula frequently projecting from near the mouth; androgynous, naked, and inclosed within a shell.
These transparent animalcules swim about upright in the sea, and wave the fins in this position as rapidly as a butterfly does its wings. Most of them are covered with a spathiform and likewise transparent shell. The branchiæ are placed externally on the body, but are not very distinct. Several species have an appendage in front of the neck, which is obviously a rudiment of the Snail's pad or sole—Flugelkracken.
The Heteropoda appear to resemble the Plantar or Sole-Snails, but the body is mostly gelatinous, and the foot or sole is only compressed to form a fin, so that they can only swim but not creep with it. Many of them have a shell almost like that of the Argonauta. Pterotracheæ—Ruderkracken.
Fam. 6. Typical Kracken, Cephalopoda or Sepiæ.
Muscular animals inclosed within a sacciform mantle, open in front; head furnished with eyes, and surrounded by more than four strong prehensile arms; laminated or leaf-like branchiæ within the mantle, sexes separate; in the body is a nephroidal or kidney-like gland, which secretes a dark-coloured or inky fluid, on which account they are called by us 'Dintenschnecken'—Sternkracken. They are obviously the highest organized Malacozoa, and already remind us strongly of Fishes, partly from their size, partly by their fleshy body, and in part by their perfect organs of vision.
The body is often as large as the trunk of a man; the head being separated from it by means of a neck, has in its interior a kind of cartilaginous brain-case or skull, with externally a pair of jaws resembling a Bird's beak, and with eyes tolerably similar to those of Fishes. Auditory organs are also present, which consist of a tympanic cavity inclosing an otolithe or ear-ossicle; nostrils are wanting. The so-called arms are perfect organs of locomotion, as also useful for seizing the prey, being provided for this purpose with sucking cups, which adhere by producing a vacuum, when applied. In other respects these arms are nothing else but the Snail's sole divided in front into lobes. The ova resemble berries, and hang attached to one another in branched clusters like a bunch of grapes. The Sepiæ possess a remarkable gland, which is complicated with the liver, and secretes a dark brown juice, which has been called ink or sepia; it probably ranks in the significance of the kidneys.
Many are covered with a shell externally, as the Nautili and Argonautæ; but in the common Sepiæ this shell adheres within the mantle upon the back, and forms a straight lamina or plate, which is sometimes horny, sometimes calcareous in its texture. It has been called the "white fish-bone." What is regarded as the dorsal side of the animal is its ventral side, because upon the former lies the pallial aperture and the anus, while the vitelline sac is also inserted there.