The porifera and coelentera . armslinviiig been removed. (From Uaeckel.) mouth is placed in the centre of the manubrium between the l)asesof the arms. In the Khizostomae, a Semostoman stage apparentlyoccurs in the development, and is followed by an incomplete con-crescence of the frilled edges of the bifurcated arms over themedian groove and the mouth ; thus, instead of a central mouth,numerous small suctorial openings, numbering often hundreds, areformed along the edges of the arm, which open by short tubes into THE SCYPHOMEDUSAE eight brachial canals, the grooves of Semostomae (Fig. 13); the
The porifera and coelentera . armslinviiig been removed. (From Uaeckel.) mouth is placed in the centre of the manubrium between the l)asesof the arms. In the Khizostomae, a Semostoman stage apparentlyoccurs in the development, and is followed by an incomplete con-crescence of the frilled edges of the bifurcated arms over themedian groove and the mouth ; thus, instead of a central mouth,numerous small suctorial openings, numbering often hundreds, areformed along the edges of the arm, which open by short tubes into THE SCYPHOMEDUSAE eight brachial canals, the grooves of Semostomae (Fig. 13); thesecanals unite into a manubrial cavity, which may either opendirectly into the gastric cavity (Rhizostoma), or, owing to theencroachment of the subgenital pits and the diagonal fusionacross its opening of the four strong pillars which support thebases of the arms, may communicate with the gastric cavity onlyby four perradial ^i/kr canals (Cannorhiza, Figs. 12, 13). The gastric cavity of the Discomedusae is generally broad and. V\\ 1.;. Diagram of a lonsitiulinal section of Cannorliiza. Lettering for both figures: ah, pcrradial arm pillar in Fig. 12, adradial arm in Fig. 13 ; ah,mass of tissue formed by the concrescence of the arm pillars ; an, suctorial mouths along the oral faces of the arms ; up, perradial arm pillar; ch, brachial canal, formed by concrescenceof its lips over the brachial groove of Semostomae; «•, circular canal; «/, arm-pillar canal;ci, interradial canal; cp, perradial canal ; ga, chamber formed by the union of the brachialcanals—the site of the mouth of Semostomae is immediately under the end of the reference line;gc, gastric cavity, cut off from ga by the encroachment of the four subgenital pits ami theirunion into the subgenital porticus ; gg, gh, gastro-genital membrane, composed above of endo-derm lining the gastric cavity and forming the generative organs, below of ectoderm lining thesubgenital iwrtieus, with niesogloea between the two ; ir, the
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
