A treatise on zoology . sterinathe inner ring is an outgrowth from the axial sinus, while each ofthe five compartments of the outer ring and canals arises separatelyas an outgrowth of the coelom, the outgrowth in the madreporicinterradius being derived from the anterior coelom, the rest from the left posterior coelom. (b) Lacunar,present in all classes except perhapsStelleroidea, and developed as lacunaeor small spaces in the connective tissue,and therefore mesodermal (Fig. XXL).It is differentiated into a network in thewall of the gut, absorbing therefrom thenutrient fluid, which is carried b
A treatise on zoology . sterinathe inner ring is an outgrowth from the axial sinus, while each ofthe five compartments of the outer ring and canals arises separatelyas an outgrowth of the coelom, the outgrowth in the madreporicinterradius being derived from the anterior coelom, the rest from the left posterior coelom. (b) Lacunar,present in all classes except perhapsStelleroidea, and developed as lacunaeor small spaces in the connective tissue,and therefore mesodermal (Fig. XXL).It is differentiated into a network in thewall of the gut, absorbing therefrom thenutrient fluid, which is carried by amain trunk on each side of the gut to acircumoral ring; from this run radialcanals, below the pseudhaemal canalswhen present, and above the water-vessels, while it is connected with net-works on the surface of both gonads andaxial organ. The lacunar system of theStelleroidea differs in the absence of anabsorbent network, and is, says Cuenot,a derivative of the axial organ, andit is only the pseudhaemal system greatly. Fio. xxir. Diagram of tlie pseudliaonialsystem of AsUrimi (after MacHride).Seen from above: M marks the Mplane ; in an<l ex, inner and outerdivisions of tlie i)erihaemal rin^ ; «,the one arising from tlie anteriorcoelom; (u, axial sinus, passiiiKtowards, but not opening into, theabf)ml perihaemal ring; , righthydrocoelfl ; g, genital strands. therefore endodermal, Respiration takes place through all exposed processes of theambulacral system, and through the body wall where thin enough,as in some Holothurians. Specialised outgrowths or foldings ofthe latter are: the external gills of Echinoidea, outgrowths ofthe circumoosophagcal sinus ; the papulae of Asteroids, containingdiverticula of the body cavity; the bnrsae of Ophiuroids; thopectini-rhombs of some Cystids ; the hydrospires of Hlastoids andsome Crinoids. Respiration is also elVectod by water entering thealimentary canal, whether through mouth or anus ; in the lattercase it is again e
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
