The porifera and coelentera . diverticula .thus formed are not, however, in anyway C()mi)arable to those seen in the oscular tube of Lcucosolctiia, since inAscnudra the folding does not affect the external surface of the body w;dl,but only the gastral layer. Modifications of the intercanal .system in the simple Clathrina type SPONGES 95 take place chiefly in one of two ways. First, in compact forms the wholesponge may be enveloped in a sort of outer covering or skin, termed apxeutlodcrvi, formed by outgrowths from the Ascon tubes situated mostperipherally; as a consequence the primitively wide
The porifera and coelentera . diverticula .thus formed are not, however, in anyway C()mi)arable to those seen in the oscular tube of Lcucosolctiia, since inAscnudra the folding does not affect the external surface of the body w;dl,but only the gastral layer. Modifications of the intercanal .system in the simple Clathrina type SPONGES 95 take place chiefly in one of two ways. First, in compact forms the wholesponge may be enveloped in a sort of outer covering or skin, termed apxeutlodcrvi, formed by outgrowths from the Ascon tubes situated mostperipherally; as a consequence the primitively wide and irregular en-trances between the outermost tubes into the intercanal system becomereduced to small orifices termed pscudo2)orcs. Secondly, the intercanalsystem may become greatly enlarged towards the centre of the sponge,forming a false gastral cavity or pscudoyaster. In consequence of thesemodifications of the intercanal system the sponge may secondarilyassume the form of an well seen in the species Clathrina. ?^«i :«?, i)seuilo(lerni; l.:c. on tlio right, should ). Schematised after Dendy. ventricosa, Carter (Fig. 6G). Here, however, the apparent ])()rc!s are reallypseudopores {j)p) leading into the intercanal system (), and the apparentgastral cavity is a pseuilogaster {), opening by a pseudosculum. Thetrue oscula (osc) open into the pseudogaster, and the wall of the vasirnrmsponge is maile up of the coiled Ascon tubes. A pseudoderm (psd) isformed towards the cavity of the pseudogaster as well as towards theexterior of the body wall. The two species Clathrina ventricosa andtripodifera offer striking examples of homoplasy, since a very similar formand structure is arrived at in perfectly dillerent ways, and the largecentral cloacae, with their excurrent orifices, are not in the least ho
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
