Before quitting the Tunicata, a few points of interest in their simple history remain to be noticed. Despite their humble organisation, they have a heart which, as may easily be ascertained in the transparent species, is subject to strange alternations of action. For after having received for a minute or two the blood _from_ the branchiæ, and propelled it _to_ the system at large, it will at once cease to pulsate for a moment or two, and then propel the blood _to_ the branchial sac, receiving it at the same time _from_ the system generally. After this reversed course has continued for some time, another pause occurs, and the first course is resumed. It is very probable that many of the Tunicata are able to hear and to see. In Chelyosoma, organs have been discovered whose structure seems to indicate that they are destined for the transmission of sound, and the Ascidiæ have frequently around the extremity of their tubes a row of coloured points similar to the imperfect organs of sight present in the majority of the bivalve Acephalans. Thus a closer examination of the lower animals is constantly bringing new faculties to light, and the further we penetrate into the secrets of their life the more we find occasion to admire the power and wisdom of their Maker! CHAP. XVI. ECHINODERMATA. STAR-FISHES, SEA-URCHINS, AND SEA-CUCUMBERS. The Star-Fishes.--Their Feet or Suckers.--Voracity of the Asterias.--The Rosy Feather-Star.--Brittle and Sand-Stars.--The real Sea-Stars of the British Waters.--The Sea-Urchins.--The Pedicellariæ.--The Shell and the Dental Apparatus of the Sea-Urchin.--The Sea-Cucumbers.--Their strange Dismemberments.--Trepang-fishing on the Coast of North Australia.--In the Feejee Islands. "As there are stars in the sky, so are there stars in the sea," is the poetical exordium of Link's treatise on Star-fishes, the first ever published on the subject; and James Montgomery tells us in rather bombastic style, that the seas are strewn with the images of the constellations with which the heavens are thronged. This is no doubt highly complimentary to the star-fishes, but is far from being merited by any particularly shining or radiant quality; as they occupy a very inferior grade among the denizens of the sea, and merely owe their stellar name to their form, which somewhat resembles the popular notion of a star. But if they are of an inferior rank to most marine animals; if even the stupid oyster boasts of a heart, which they do not possess; yet a closer inspection of their organisation shows us many wonderful peculiarities, and proves to us once more that nature has impressed the stamp of perfection as well upon her lowest and most simple creations, as upon those beings that rank highest in the scale of life.