. A manual of zoology. Zoology. HYDROZOA 213 snaky fashion, whence the name medusa. Circular striped muscles run on the suljumbrellar side of Ijell and velum, causing the characteristic motion. By their contraction the bell becomes more arched and narrowed, while the velum (which hangs down when at rest—fig. 175, .4) contracts like a diaphragm across the mouth of the Ijell (B). Since water is thus forced out through the opening the medusa is forced forward lay the reac- tion. The circular muscles of the umbrella and velum are separated. Fig. 176.—Tiara pileata (after Haeckel, from Hatschek). b
. A manual of zoology. Zoology. HYDROZOA 213 snaky fashion, whence the name medusa. Circular striped muscles run on the suljumbrellar side of Ijell and velum, causing the characteristic motion. By their contraction the bell becomes more arched and narrowed, while the velum (which hangs down when at rest—fig. 175, .4) contracts like a diaphragm across the mouth of the Ijell (B). Since water is thus forced out through the opening the medusa is forced forward lay the reac- tion. The circular muscles of the umbrella and velum are separated. Fig. 176.—Tiara pileata (after Haeckel, from Hatschek). by two nerve rings, one siihnmbrellar, the other exttmbrcUar in position (fig. 177, w\ «=), the first supplying the muscle plexus, the other the sensory organs—eyes of the simplest type, red pigment spots with or with- out a lens; and open or closed statocysts ('ears'). Tactile hairs are abundant on the tentacles. The statocysts are of two types, both beginning as open organs and reaching their highest development as closed vesicles. One type, the tentacular organs, occurs in the Trachymedusae (fig. 177, 1-4) the other, or velar organ, in the Leptomedusffi (5-6). The tentacular organs are modified tentacles, the ento-. 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
