. Elements of zoölogy. Zoology. WHEEL-ANIMALCULES. 45 aquaticus is the thread-worm, common in many insects and in pools. They are the so-called horse-hairs that do not turn to snakes. Class III.—Wheel-Animalcules (Rotifers). The Rotifers (Fig. 44) are microscopic worms, some being only Tf-g- of an inch in length, having a membranous covering. Upon the anterior por- tion they have one or two disks, surrounded by cilia (Fig. 44, A), whose constant motion creates the optical illusion of wheels re- volving. They abound in the ocean, and in standing fresh wa- ter, and are so tenacious of life that
. Elements of zoölogy. Zoology. WHEEL-ANIMALCULES. 45 aquaticus is the thread-worm, common in many insects and in pools. They are the so-called horse-hairs that do not turn to snakes. Class III.—Wheel-Animalcules (Rotifers). The Rotifers (Fig. 44) are microscopic worms, some being only Tf-g- of an inch in length, having a membranous covering. Upon the anterior por- tion they have one or two disks, surrounded by cilia (Fig. 44, A), whose constant motion creates the optical illusion of wheels re- volving. They abound in the ocean, and in standing fresh wa- ter, and are so tenacious of life that they recover after having been dried for years, their sud- den appearance after continued droughts being attributed to what is called spontaneous generation. Under the microscope they as- sume remarkable shapes : now oval, caused by the upper and lower segments shutting togeth- er ; then leech-like, moving along seemingly by suckers, or darting off swiftly, propelled by cilia. They are oviparous, and Ehren- berg found that one species pro- duced 16,000,000 young in twelve Fig. 44.—A Rotifer, highly- magnified {Hydatina sen- fa). A, cilia ; a, anus ; d, contractile vesicle ; c, water-vessels ; e, ovary ; /, ganglion. Class IV.—Moss Animals (Polyzoa). These animals form a moss or coral-like growth, com- posed of cells (Fig. 45), each of which contains a minute,. 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
