Mysis chamæleon.
The Opossum Shrimp belongs to a group of crustaceous animals which have been called fissipeds, (split-feet,) on account of each of their feet being divided nearly throughout its whole length; the inner limb being constructed for progression and the seizing of their prey, and the outer for swimming and giving that motion to the water which is essential to the organs of breathing, which are, as it were, wrapped round the base of each limb, and fully exposed to the action of the element. In the other Crustacea, which they most nearly approach, such as shrimps, prawns, &c., there is a single row of five feet on each side: but the genus we are now describing possesses as many as four rows of feet, each containing eight, so that in all, the number of feet amounts to as many as thirty-two,—sixteen adapted for swimming, and sixteen for seizing their prey. In consequence of this organization, the Shrimps seek their food in the sands at the bottom, while the present genus frequent the surface.
The most singular portion of their formation, and that to which they are indebted for a name, is a kind of pouch which the female possesses, fixed beneath the body, and formed of two concave pieces of shell; this pouch, which is very capacious, considering the size of the animal, is destined to receive the eggs, which are deposited in it, enveloped in a kind of jelly-like substance, most probably forming the food of the young when first hatched. As fast as the young assume the lengthened form of the perfect animals, they are found to arrange themselves in this pouch closely and regularly side by side, with their heads towards the breast of the mother. After this manner they lie closely compacted together, and present a perfectly symmetrical arrangement, easily observed from the translucency of the valves of the pouch, and the large size and blackness of their eyes. The males of the Opossum Shrimp are not so numerous as the females, and are without the singular pouch we have described.
We have already noticed the fact of these Shrimps being the food of the Greenland whale, in the northern seas, but in these climates they serve as food for herrings.
It is in looking closely into the structure of these little animals that we see the perfection of the Divine Artist. Nature’s greater productions appear coarse indeed to these elaborate and highly-finished master-pieces, and in using more and more powerful magnifiers we still continue to bring new parts and touches into view. If, for instance, after observing one of their members with the naked eye, which has informed us that the part we have been examining is composed but of one piece, we employ a magnifying glass with a low power, the same part appears jointed, or composed of several pieces articulated together. Employing a higher magnifier, it appears fringed with long hairs, which, on further scrutiny, seem to be themselves fringed with hairs still more minute; many of these minute parts also, are evidently jointed, and perform sensible motions. But what idea can we form of the various muscles which put these parts in movement, of the nerves which actuate them, and the vessels which supply them with the nourishment necessary for growth and support, and which we know, from comparison with other creatures, they must possess!
The [Opossum Shrimps], we have seen, are the prey of the larger inhabitants of the deep; but they, in their turn, destroy others that are smaller than themselves,—seizing upon every animal substance they are able to manage that comes within their reach, and, if placed in a vessel of sea-water by themselves, devouring each other.
The species represented in the engraving has been called the Mysis chamæleon, from its colour varying according to the substances on which it feeds, through all the gradations of gray, black, brown, and pink.
ORDER CRUSTACEA HETEROBRANCHIÆ.
(Crustacea with Organs of Breathing variously
placed, never concealed.)