. Cassell's natural history. Animals; Animal behavior. THE LlTUlSTIhJE. ^t^M^^Mi. Fig. The Monaxouidre are cosmopolitan, chiefly shallow-water forms. They range from the strand-line down to 862 fathoms ; on the evidence of Cliona borings in Silurian fossils they are concluded to have been in existence in early Palseozoic times; fossil remains of their skeletons are rare, rharetrosponijia stra/iani (Sollas) of the Cambridge Greensand, a large Renierine Sponge with a tibrous skeleton, being the best preserved and most certainly demonstrated example yet known. Ti-h-((c/iiieUidce*—This sub-or
. Cassell's natural history. Animals; Animal behavior. THE LlTUlSTIhJE. ^t^M^^Mi. Fig. The Monaxouidre are cosmopolitan, chiefly shallow-water forms. They range from the strand-line down to 862 fathoms ; on the evidence of Cliona borings in Silurian fossils they are concluded to have been in existence in early Palseozoic times; fossil remains of their skeletons are rare, rharetrosponijia stra/iani (Sollas) of the Cambridge Greensand, a large Renierine Sponge with a tibrous skeleton, being the best preserved and most certainly demonstrated example yet known. Ti-h-((c/iiieUidce*—This sub-order embraces two very different groups; the Choristichf, in wliicli the spicules are separate from each other, and the Lithistidw, in which they are united by the interlocking of their branched ends into a dense stony network. In the Chorlsfidmf are united a number of very different types of SpongeSj of which the Geodina are best known. In these the body, usually more or less spherical, is differ- enced into an external rind and an inner mark, or paren- chyma, like an orange ; the rind (Fig. 15) consists of a layer of fibrous connective tissue, covered by the ecto- derm and a layer of minute flesh-spicules; its outer two- thirds is crammed full of spicules, usually trichite-globules '''i^V',"i,';l';™|^^'™;'[^.'|;]y,\?j;j^;j|^j';jf'!^ (mistaken by Bowerbank for ova), which give to it great firmness and consistency. The incurrent canals in their passage through the rind present a very definite, usually hour-glass form, the constricted part being defended by a sphinctral muscle, produced by a modification in the character of the surrounding fibrous layer. The chief spicules are large acerates, which lie in bundles or fibres radiating towards the surface, near which some of them divide into three rays, forming forks and anchors. The —Notwithstanding the firmness of their coral-like skeleton these are no more characterised by constancy of form t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjecta, booksubjectanimals
