A pulsatory vessel near the gullet propels the yellow blood into a system of fine tubes, that are spread over the walls of the stomach and its rays. Through these walls the blood receives a nutritious liquid, which it carries with it into a network of capillary vessels, widely extended throughout the body, being propelled by the contractile powers of the vessels themselves, and after having supplied the tissues with nourishment, it is carried by tubes to the point from whence it started, to begin a new course. The capillary network passes immediately under a portion of the skin of the star-fish, through which an exchange of the respiratory gases takes place. Besides, the star-fishes breathe the sea-water through numerous conical tubes, that project in patches from the back. Through these tubes, which can be opened and shut, the water is readily admitted into the cavity containing the digestive organs, with which they are in communication. The star-fish slowly distends itself with water, and then gives out a portion of it, but at no regular time. The cavity is never empty of water, and as its lining is densely bristled with cilia, their vibrations keep the vascular surface of the digestive organs perpetually bathed with the respiratory medium. The star-fishes have a radiating system of nerves suited to their form. A ring of slender nerve-cords surrounds the mouth, from whence three nerves are sent off at the commencement of each ray: two of these, which are filaments, go to the organs in the central disk, while the middle one, which is a great trunk, passes through the centre of the rays, and terminates in a nerve-centre, or ganglion, placed under a coloured eye-speck at their extremity. The structure of the rays, the eye-specks, and the nerve-centres below them, are so similar, that they are merely repetitions of one another; hence no nerve-centre can control the others, but they are all connected by the ring encircling the mouth, which is a common bond of communication. How far the movements of these animals indicate sensation we have not the power to determine, but they feel acutely, for the mouth, the feet, and especially the pedicellariæ, are highly sensitive, and shrink on the least touch. The eye-specks are probably sensitive to light, and as the star-fishes often feed on putrid matter, they are supposed to be endowed with the sense of smell.