. Text-book of zoology for schools and colleges. Zoology. 170 INVERTEBKATE ANIMALS. the body. On the other hand, in the Sydrozoa, there is no alimentary canal distinct from the body-cavity, there is no nervous system, and the reproductive organs are in the form of external processes of the Fig. 77.—1. Fragment of Flustra tmneata, one of the Sea-mats, natural size. 2. A single polypide of Valkeria, tnagmfled, showing the circular crown of tentacles. S. A polypide of ZopTwpns crystalH7iu3, a. fTesh-v/aXer'Po]yzol!iii^ highly magnified, showing the horse- shoe shaped crown of tentacle
. Text-book of zoology for schools and colleges. Zoology. 170 INVERTEBKATE ANIMALS. the body. On the other hand, in the Sydrozoa, there is no alimentary canal distinct from the body-cavity, there is no nervous system, and the reproductive organs are in the form of external processes of the Fig. 77.—1. Fragment of Flustra tmneata, one of the Sea-mats, natural size. 2. A single polypide of Valkeria, tnagmfled, showing the circular crown of tentacles. S. A polypide of ZopTwpns crystalH7iu3, a. fTesh-v/aXer'Po]yzol!iii^ highly magnified, showing the horse- shoe shaped crown of tentacles: a Tentacular crown; & Gullet; cStonjach; c^ Intestine; 6 Anus; (/Gizzard; /cEndocyst; 2 Ectocyst. The foregoing gives the essential structure of the polypide of any Pdlyzoon, but in nature this simplicity is lost. In all cases in nature the primitive polypide possesses the power of producing fresh zoQids by a process of budding; and these zo6ids remain attached to one another, so that ultimately there is produced a compound growth or colony. Further, in almost all the Polyzoa, the outer layer of the polypide is more or less hardened by the deposition in it of chitine or of carbonate of lime. The skeletons thus formed are the parts of the colony which are most familiarly known, and in the case of the com- mon Sea-mats (Fig. 77, 1) they are very well known to sea- side visitors, and are generally regarded as sea-weeds. Exam- ined in its dead state, such a skeleton only shows a number of little horny chambers or cells (Fig. 76, 1), each with a little aperture. When alive, however, each of these cells was ten- anted by a single zoOid or polypide, capable of protruding its. 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 Nicholson, Henry Alleyne, 1844-1899. New York, D. Appleton and Co.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
