. Zoology : for students and general readers . Zoology. ORAPTOLITES. 61 there is no trace of a nervous system such as exists in Sarsia, where nerve-fibres extend around the margin and along the radial tubes (Romanes). In the groups of Campamclarim, represented by Plumu- laria, Sertularia, Zygodactyla, Dynamena, and Campanu- laria, the ectoderm is protected by a horny or chitinous sheath (perisarc) enveloping the zooids. The Hydroids re- tract,-vvhen disturbed, into small cells (hydrothecce), arranged in opposite rows on the stalk as in Sertu- laria (Fig. 42), or singly at the ends of the stalk
. Zoology : for students and general readers . Zoology. ORAPTOLITES. 61 there is no trace of a nervous system such as exists in Sarsia, where nerve-fibres extend around the margin and along the radial tubes (Romanes). In the groups of Campamclarim, represented by Plumu- laria, Sertularia, Zygodactyla, Dynamena, and Campanu- laria, the ectoderm is protected by a horny or chitinous sheath (perisarc) enveloping the zooids. The Hydroids re- tract,-vvhen disturbed, into small cells (hydrothecce), arranged in opposite rows on the stalk as in Sertu- laria (Fig. 42), or singly at the ends of the stalks, as in Cam- panularia, while the sheaths (gonothecm) protecting the medu- sa-buds are distin- guished by their much larger size and cup-shaped form. The Sertularians abound on sea-weeds, and may be recogniz- ed from their resem- blance to mosses. They are among the most common objects of the seaside. The medusse of these and many other Hydroids can be collected by a towing-net, and emptied into a jar, where they can be de- tected by the naked eye after a little practice. Graptolites.—More nearly allied perhaps to the Sertularian Hydroids than any other known animals are the Graptolites (Fig. 43), which were most abundant in the Lower Silurian period, and lingered as late as the Clinton epoch of the Upper Silurian. In OraptolUhus Logani the hydroid colony (hy- drosome) is a long narrow blade, with a row of cells on one. Sertularia abletina of Europe. A, natural 6ize; B. magnified, showing the hydrarium, with tlie cells.—From Macalliwter. Fig. 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 Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
Size: 1352px × 1848px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
