The royal natural history . toits arrangement in a star-fish, or regular sea-urchin; but the system occurs, withvarious modifications, in all Echinoderms, and is one of the features that separatethe group from other animals. The Echinoderms are also peculiar in the possession of three, or perhaps four5different systems of nerves, of which three, or at least two, are present at the sametime. One system supplies the skin, the tube-feet, and the intestine ; its chief partsbeing a ring round the mouth, and radial nerves radiating therefrom. The secondsystem has a similar arrangement, but lies deep
The royal natural history . toits arrangement in a star-fish, or regular sea-urchin; but the system occurs, withvarious modifications, in all Echinoderms, and is one of the features that separatethe group from other animals. The Echinoderms are also peculiar in the possession of three, or perhaps four5different systems of nerves, of which three, or at least two, are present at the sametime. One system supplies the skin, the tube-feet, and the intestine ; its chief partsbeing a ring round the mouth, and radial nerves radiating therefrom. The secondsystem has a similar arrangement, but lies deeper, and supplies the internalmuscles of the body-wall. The third system, which is most fully developed incrinoids, starts from the other side of the body, opposite to the mouth, and suppliesthe muscles that work the arms and stem. If the arm of a star-fish be openedfrom the back, there will be seen a pair of pleated extensions from the these be removed, there will be exposed a pair of orange-coloured tubes, some-. DIAGRAJI OF AMBULACRAL SYSTEM OF A STARFISH. /, Small swellings connected with the tulie-feet ; k, The radial canal withwhich they unite ; e, Ring-canal into which the radial canals open ;c, d, Membranous sacs that serve as reservoirs for water from radialcanals ; a, Stone-canal, leading from ring-canal to the madreporite,n; m, Mouth. GENERAL CHARACTERS. 293 what branched and knotty, which communicate with the exterior at the anglesbetween the rays. These are the generative glands. In all Echinoderms, exceptsea-cucumbers, these glands are affected by the radiate structure of the animals; incrinoids the generative products are even produced in the extremities of the of Having glanced at those points of structure in which Echinoderms the classes, resemble one another and differ from the rest of the animal kingdom,we may shortly examine the main characters in which a sea-urchin, a star-fish, acrinoid, a brittle-star, and a sea-cucumber differ
Size: 1754px × 1424px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
