. An introduction to zoology : for the use of high schools . A peculiar kind of bud-ding occurs in the fresh-waterSponges, which recalls the form-ation of the winter-buds of thePolyzoa, as it takes place undersimilar conditions. The budsare called statoblasts or gem-mules and are protected bycharacteristic spicules (Fig. 188), 10. Fossil Iemains of spongesare abundant in the earlier for-mations, but they reached theheiglit of their developmentduring the upper Secondaryperiod. Fig. of a Calcareoussponge, with a single osculum. a, ectoderm ; 6, mesoderm, with trira-diate spicules;
. An introduction to zoology : for the use of high schools . A peculiar kind of bud-ding occurs in the fresh-waterSponges, which recalls the form-ation of the winter-buds of thePolyzoa, as it takes place undersimilar conditions. The budsare called statoblasts or gem-mules and are protected bycharacteristic spicules (Fig. 188), 10. Fossil Iemains of spongesare abundant in the earlier for-mations, but they reached theheiglit of their developmentduring the upper Secondaryperiod. Fig. of a Calcareoussponge, with a single osculum. a, ectoderm ; 6, mesoderm, with trira-diate spicules; c, lining of gastro-vascu-lar cavity ; f, ciliated chambers lined with collar-cells^e osculum TheJ,nows f found iu shallow water ; the indicate the direction of the current in- wards through the pores, and outwards same is true of the fleshy Non-cal- 11. The Calcarea are chiefly minute through the osculum. others attain a considerablesize. Some of those withpurely siliceous skeletons,like Euplectella and Hyalo- carea—Halisarca,—but most of the .4. nema, are most beautiful k J objects ; they occur in the ~~jdepths of the ocean, anchor- l-^^\ing themselves in soft mudby a wisp of glassy threads. VfIn these foi-ms, there aretriaxial spicules in additionto the fibres, but in many cjTioTicrps from shallow wnter ^S- 188.—Diagram of gemmule of a fresh-water sponges trom SUallOW water, gp^^.e, showing the coating of amphidislts and the the spicules alone constitute aperture ; b, an amphidisk of Ephydatia- the river the skeleton, which may ^1°^ * 252 HIGH SCHOOL ZOOLOGY. then be cork-like {Siiberites) or friable in consistence (Si^cmgiUa). Onegenus—C/(0HO—has the singular habit of boring by means of its spiculainto limestone and shells. The sponges of commerce, which come chieflyfrom the ^lediterranean and the Bahamas, have the skeleton of spongin,either entirely free from foreign matter (in the best Turkey sponges—Emponfjia olJicinaUs), or else somewhat coarser in tex
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
