Outlines of zoology . inhalant canals,flagellate chambers, agastrula forming in themesogloea, etc. STRUCTURE OF SPONGES. 127 easily and well. Like plants, they form buds, the outcomeof surplus nourishment. These buds, like the suckers ofa rose-bush, often ac-quire some apparentindependence, and- thesponge looks like manyvases, not like , as they growthese buds may fuse,like the branches of atree tied closely to-gether. Thus the struc-ture becomes more in-tricate. ib) In the simplesponge the cavity of thevase is completely linedby the collared flagellatecells {Ascon type). Butthe in
Outlines of zoology . inhalant canals,flagellate chambers, agastrula forming in themesogloea, etc. STRUCTURE OF SPONGES. 127 easily and well. Like plants, they form buds, the outcomeof surplus nourishment. These buds, like the suckers ofa rose-bush, often ac-quire some apparentindependence, and- thesponge looks like manyvases, not like , as they growthese buds may fuse,like the branches of atree tied closely to-gether. Thus the struc-ture becomes more in-tricate. ib) In the simplesponge the cavity of thevase is completely linedby the collared flagellatecells {Ascon type). Butthe inner layer may growout into radial chambersto which the choan-ocytes are restricted{Syion type), and thewalls of these may alsobe folded into side aisles(Leucon type). The out-growing ? of the innerlayer into the mesogloeamay be continued evenfurther, and the cellsmay become pavement-like except in theminute flagellate cham-bers, where alone thecharacteristic choano-cytes are retained (seeFig. 60). It may be that the. Fig. 60. — Diagram showing types ofcanal system. — After Korschelt andHeider. The flagellate regions aredark throughout, the mesoglcea isdotted, the arrows show the directionof the currents. All the figures re-present cross-sections through the wall. A. Simple Ascon type {Ec, outer layer; En., inner layer; jT^., mesoglcea). B. Sycon type, with flagellate radial chambers (•?^•). . C. Leucon type, with flagellate side, aisles on the main radial chambers. D. Still more complex type, with small flagel- late chambers (). characteristic folding or outgrowth of the inner layer isnecessitated by the fact that the component cells are better 128 PHYLUM PORIFERA SPONGES. nourished and multiply more rapidly than those of theouter layer. (c) By infoldings of the outer layer and a subjacentsheath of mesoglcea^-subdermal spaces may be formed;an outer cortex may be distinctly differentiated from theinternal region in which the flagellate chambers occur; thepores may c
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
