The royal natural history . holes pass the tube-feet,which are all provided with suckersat the end. These latter zones are,therefore, the ambulacral zones; oneof them being seen in the middle of the illustration. The other zones are calledinterambulacral, and one of them is shown on the left of the same illustration. Allthe zones converge towards the summit of the test, where the vent is situatedin a circular space covered with membrane. This membrane contains a fewirregular granules, and is surrounded by five large interradially placed plates,pierced by the ducts of the generative glands. One
The royal natural history . holes pass the tube-feet,which are all provided with suckersat the end. These latter zones are,therefore, the ambulacral zones; oneof them being seen in the middle of the illustration. The other zones are calledinterambulacral, and one of them is shown on the left of the same illustration. Allthe zones converge towards the summit of the test, where the vent is situatedin a circular space covered with membrane. This membrane contains a fewirregular granules, and is surrounded by five large interradially placed plates,pierced by the ducts of the generative glands. One is also pierced by a largenumber of small water-pores, and is called the madreporite. Outside these fiveplates, and alternating with them, are five other plates, each situated at the top ofan ambulacral zone, and pierced by the unpaired tentacles, which terminate thewater-canals, and rejoresent the unpaired tentacles near the eye at the ends of thearms of a star-fish. At the other pole of the body is another membrane, sur-. TEST OF EDIBLE SEA-URCHIN, WITH THE SPINES REMOVEDFROM THE LEFT-HAND HALF (nat. size). SEA-URCHINS. 3°9
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
