. Animal forms; a second book of zoology. Zoology. and a portion of the locomotor system; but some species, at least, renew them again. In some of the starfishes and brittle-stars portions of the body appear to be voluntarily de- tached and to develop into new individuals, and it is thought that such self-mutilation is a normal method of reproduction. 140. Locomotor system.—One of the most characteristic and remarkable features of the echi- noderms is the water-vascular system, a series of vessels con- taining water which serve in the process of locomotion. Their arrangement and mode of opera-
. Animal forms; a second book of zoology. Zoology. and a portion of the locomotor system; but some species, at least, renew them again. In some of the starfishes and brittle-stars portions of the body appear to be voluntarily de- tached and to develop into new individuals, and it is thought that such self-mutilation is a normal method of reproduction. 140. Locomotor system.—One of the most characteristic and remarkable features of the echi- noderms is the water-vascular system, a series of vessels con- taining water which serve in the process of locomotion. Their arrangement and mode of opera- tion are, with slight modifica- tions, the same throughout the group, and may be readily un- derstood from their study in the starfish. On the dorsal surface of a starfish, in the angle between two of the arms, is a round, slightly elevated, calcareous plate, the madreporic body (Fig. 95, ), which under the microscope appears full of holes, like the " rose " of a watering-pot. This connects with a tube that passes to the opposite side of the body, where it enters a canal completely encircling the mouth. On this ring-canal a number of sac-like reservoirs with muscular walls are at- tached, and from it a vessel extends along the under sur- face of each arm from base to tip. Each of these radial water-mains gives off numerous lateral branches that open out into small reservoirs similar to those located on the ring-canal, and a short distance beyond communicate through the wall of the body with one of the numerous. Fig. 92.—Sea-cucumber {Cucu- maria sp.). Natural Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Jordan, David Starr, 1851-1931; Heath, Harold, 1868- [from old catalog] joint author. New York, D. Appleton and company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
