The royal natural history . phial-shaped fourtalesia ; test with spines removed (enlarged 4 times). plished not by any acid secretion,—for on the west coast of Africa an Echinornetrahas been found boring into an augite lava,—but by the continuous movement of theteeth and spines. The common Strongylocentrotus is a well-known example of aboring sea-urchin. When the waves wash up against the urchin it sets its spinesrigidly against the sides of its hole and so holds fast. Although most of the sea-urchins have a rigid test, yet there are some inwhich the plates are only loosely joined together, so
The royal natural history . phial-shaped fourtalesia ; test with spines removed (enlarged 4 times). plished not by any acid secretion,—for on the west coast of Africa an Echinornetrahas been found boring into an augite lava,—but by the continuous movement of theteeth and spines. The common Strongylocentrotus is a well-known example of aboring sea-urchin. When the waves wash up against the urchin it sets its spinesrigidly against the sides of its hole and so holds fast. Although most of the sea-urchins have a rigid test, yet there are some inwhich the plates are only loosely joined together, so that the test is leather-urchin (§ nat. size). This is the case in an Astropyga ; but is still more pronounced in the leather-urchin (Asthenosoma), and other members of the family Echinothuridce. Re-spiration is effected in the regular sea-urchins by ten gills near the are thin-walled ciliated extensions of the body-cavity protruding 312 ECHINODERMS. between the membrane round the mouth and the plates of the test. In theirregular urchins some tube-feet are modified for respiration, becoming broad,flat, and somewhat lobed; the hinder end of the intestine seems to be respiratoryin function. Some sea-urchins possess eyes. In a Diadema there are fiveovate pigment-masses of a brilliant ultramarine blue, placed at ecpaal distancesaround the vent. There are certain other peculiar bodies supposed to be sense-organs of some kind, called sphseridia, which are of microscopic size, and instructure not unlike tiny spines. They lie near the mouth and on the lowerambulacral plates, are often set in smal
Size: 1796px × 1391px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
