surface of their skin, where the tiny creatures fix themselves by means of strong cables. Fig. 7 represents a species that lodges on the cod, and it in its turn affords a resting-place for another form—the Udonellœ.
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| Of the Natural Size. | Caligulus Elegans. Female. | |
| Fig. 7. | ||
A curious creature, with an equally curious function, that entitles it to a place among mutualists, was discovered some years ago among the eggs of the lobster, by Van Beneden, who thus describes it: "It is known that lobsters, as well as crabs, and the greater part of the Crustacea, carry their eggs under the abdomen, and that these eggs remain suspended there until the embryos are hatched. In the midst of them lives an animal of extreme agility, which is, perhaps, the most extraordinary being that has been subjected to the eyes of the zoölogist. It may be said, without exaggeration, that it is a biped, or even quadruped, worm. Let us imagine a clown from the circus, with his limbs as far dislocated as possible, we might even say entirely deprived of bones, displaying tricks of strength and activity, on a heap of monster cannon-balls which he struggles to surmount; placing one foot, formed like an air-bladder, on one ball, the other foot on another, alternately balancing and extending his body, folding his limbs on each other, or bending his body upward like a caterpillar of the Geometridœ, and we shall then have but an imperfect idea of all the attitudes which it assumes, and which it varies incessantly. It is neither a parasite nor a messmate; it does not live at the expense of the lobster, but on one of the productions of these crustaceans, much in the same manner as do the Caligi and the Arguli. The lobster gives him a berth, and the passenger feeds himself at the expense of the cargo; that is to say, he eats the eggs and the embryos which die, and the decomposition of which might be fatal to his host and his progeny. These Histriobdellœ have the same duty to perform as vultures and jackals, which clear the plains of carcasses. That which causes us to suppose that such is their appropriate office is, that they have an apparatus for the purpose of sucking eggs, and that we have not found in their digestive canal any remains which resemble any true organism."
