Image from page 37 of “Outlines of zoology” (1916) – more Marine Life goodness curated by www.SardineRunPE.co.za
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Title: Outlines of zoology
Year: 1916 (1910s)
Authors: Thomson, J. Arthur (John Arthur), 1861-1933
Publisher: New York, Appleton
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN
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Text Appearing Before Image:
he conditions are different,■as may be expressed in the following table:— Sponges and Ccelentkra. Higher Animals (Ccelomata). There is no body cavity. There is butone cavity, that of the food canal. Except in ctenophores, there is nodefinite middle layer of cells (meso-derm), but rather a middle jelly(mesogloea), and the embryo isdiploblastic. The radial symmetry of the gastrulaembyro is usually retained in theadult, and the Jongitudinal (oral-aboral) axis of the adult correspondsto the long axis of the gastrula. There is a body cavity or coslom be-tween the food canal and the body-wall. But this is often incipient, ordegenerate. There is a distinct middle layer of cells(mesoderm) between the externalectoderm and the internal endo-derm. The embryo is triploblastic. The adults are usually bilateral, in somecases asymmetrical, in echinodermssuperficially radial. Coelentera.—This series includes jelly-fisties, sea-anemones,corals, zoophytes, and the like, most of which are equipped
Text Appearing After Image:
-Sea anemones on back of heimit crab,—After Andres. – ■with stinging cells, by means of which they paralyse theirprey. All but a few are marine. The body may be aitubular polyp, or a more or less bell-like medusoid, and PORIFERA. 13- in some cases the two forms are included in one life cycle.Budding is very common, and many of the sedentary forms-—corals—have shells of lime. Porifera.—Sponges, or Porifera, are the simplest many-celled animals. In the simplest forms, the body is atubular, two-layered sac, with numerous inhalant pores \>jwhich water passes in, with a central cavity lined by cellsbearing lashes or flagella, and with an exhalant apertureBut budding, folding, and other complications arise, andthere is almost always a skeleton, calcareous, siliceous, orhorny. Apart from one family (Spongillidse), all sponges-are marine. Contrast of IVEetazoa and Protozoa.—All the animals hitherto-mentioned have bodies built up of many cells, but there are other,animals, each
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