. Elements of zoölogy. Zoology. SEA- C UC UMBERS. 39 madreporic plate, w h, and a similar circulatory system are found as in the star-fishes. Development.—They are produced from eggs, the free- swimming young passing through many changes (Fig. 37). In some Echini the young are pro- duced without changes. The Her- miaster holds its young in a regular sac, while the eggs and young in others are held in place by the spines that fold about them like so many protective arms. Class IV. — Sea-Cucumbers {HolotJmroidcd). In these animals (Fig. 38) the body is long and worm-like, and resembles a rough-s
. Elements of zoölogy. Zoology. SEA- C UC UMBERS. 39 madreporic plate, w h, and a similar circulatory system are found as in the star-fishes. Development.—They are produced from eggs, the free- swimming young passing through many changes (Fig. 37). In some Echini the young are pro- duced without changes. The Her- miaster holds its young in a regular sac, while the eggs and young in others are held in place by the spines that fold about them like so many protective arms. Class IV. — Sea-Cucumbers {HolotJmroidcd). In these animals (Fig. 38) the body is long and worm-like, and resembles a rough-skinned cucum- ber. Looking down upon the mouth, that is surrounded by ten- tacle-like gills, their radiate char- acter is seen, and by laying open the body a similar disposition of muscles may be noticed. The madreporic plate or strainer is in- ternal. The feet are in five se- ries, each consisting of five rows, by which they move slowly along. The skin of Holothurians is leathery, and contains num- bers of curious bodies resembling dumb-bells, wheels, and anchors (Fig. 39). The Holothuria Floridiana is in- habited by a fish, the Fierasfer* In the Holothuria sea- * In many observed by the author on the Florida reef they invariably died as soon as taken from the Holothurians ; but in the aquarium at Naples they have been seen to leave their home and return tail first, the action of the Holothurian in taking in water helping them Fig. 37.—Development of sea - urchin. A, free- swimming young ; 0, #, lime rods ; b, urchin forming within. B, later form, showing 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 Holder, Charles Frederick, 1851-1915; Holder, Joseph Bassett, 1824-1888, joint author. New York : D. Appleton and company
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
