. Elementary text-book of zoology [electronic resource]. Zoology. ANNUL A7 A. a pair of otocysts. These are situated laterally on the peris- Sensory tomium and are supplied by nerves from the brain. They consist of spherical sacs communi- cating with the exterior by fine ducts. The cells lining the Fig. 113.—Section through the Otocyst of Arenicola. (After AsHWOKTH and Gamble.). sac are sensory and the cavity contains a number of loose concretions or otolitJis which appear to be sand-grains. On the prostomium is a ciliated pit called the nuchal- organ^ a probable sense-organ allied to the pair
. Elementary text-book of zoology [electronic resource]. Zoology. ANNUL A7 A. a pair of otocysts. These are situated laterally on the peris- Sensory tomium and are supplied by nerves from the brain. They consist of spherical sacs communi- cating with the exterior by fine ducts. The cells lining the Fig. 113.—Section through the Otocyst of Arenicola. (After AsHWOKTH and Gamble.). sac are sensory and the cavity contains a number of loose concretions or otolitJis which appear to be sand-grains. On the prostomium is a ciliated pit called the nuchal- organ^ a probable sense-organ allied to the paired ciliated pits of Polygordiys. Arenicola has no prostomial tentacles, but the prostomium is produced into two lobes which are also probably sensory. The muscular system is well developed and consists of Muscular ^ circular layer under the ectoderm and a longi- tudinal layer inside it. There are also diagonal fibres running from the lateral lines to the mid-ventral line. Nearly all the animals usually called " worms " move by the system of circular and longitudinal muscles. The body of the " worm" which contains coelomic fluid acts much like an elongated bladder or sausage- skin filled with fluid. When the circular muscles conti act they press on the coelomic fluid which forces out each end and hence elongates the worm, reducing its calibre. When the longitudinal muscles contract the body is sh(jrtene(l, the crelomic fluid at the same time forcing the walls outwards. Ilence the alternate movements of the two muscular. 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 Masterman, Arthur Thomas; Parsons, John Herbert, Sir, 1868-1957, donor; S. H. Lazarus (Firm); University College, London. Library Services. Edinburgh : E. & S. Livingstone
Size: 2097px × 1192px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1901
