3485. The first have not yet attained to the unity or single character of the mouth, but imbibe their food through numerous tubes. They are bundles of ramified Vorticellæ, a thoracic duct full of glands and roots, which absorbs nutriment out of the sea, instead of an intestine.
As the first family they are the antetypes of the Mussels and Entozoa, and especially of the Hydatids and Tape-worms, and we shall not be far from hitting the mark, if we compare their air-bladder with the hindermost cystiform member of the body in the Hydatids.
3486. The second family have a single mouth and ribs mostly full of lamellæ, which are probably the antetypes of gills; they are also frequently traversed by nutritive vessels.
They are antetypical of Snails, being in form an abdominal pouch, in substance a liver, and frequently possessing paired tentacula. Higher up, and they indicate the Crabs.
3487. The third have, as a general rule, one central mouth surrounded by four arms and very numerous vessels, which run from the gastric cavity to its margins, and there mostly elongate into filaments or hairs, being thus true lymphatic vessels, which convey the nourishment directly from the stomach through the whole body, and become on its margin tentacula.
3488. As antetypes of the Kracken they particularly manifest the form of the Sepiæ, or Cephalopods, in the strong and frequently papillated arms that surround the mouth. Gland-like nodes are also developed in the margin of the pileus, but their meaning is as yet doubtful. Upon a higher stage, and they are antetypical of Insects.
Their vascular system forms an exceedingly regular, quaternary net, with branches and ramules ranging opposite to each other, which have been believed to be the vitelline network of the ovum when hatched. These vessels terminate likewise in a common marginal vessel, as in the vitellus.
3489. Viewed as a whole they resemble in form, appendages, and substance the fœtal involucra or envelopes. The upper surface may be compared with the convex back of the envelopes, the lower to the concave funnel of the umbilical cord, and the succigerent filaments or hairs to the shags of the chorion. They are probably elongated by injection, like the so-called legs of the Star-fishes.
The secretion of the ova in four ovaries speaks also in favour of their higher grade of development. They lie in four cavities around the stomach, which also open near to the mouth. Their size also is significantly expressive of their higher position.
Finally, they are of separate sexes. In them is the milt for the first time distinctly displayed, and in the same situation indeed where in other animals the ovaries are.