The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . nchial sac. TUNICATA 381 and directly continuous with that layer through the atrialaperture (fig. 6); consequently the mantle is covered both,^ externally and internally by / * ,.ft» ectodermal cells. •vA/^i / There is no true body I [^ cavity or coelom in the mesoderm; and yet the Tuni-cata are Coelomata in theirstructure and affinities, al-though it is very doubtfulwhether the enterocoelewhich has been described inthe development is reallyfound. In any case thecoelom if formed is after-wards sup
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . nchial sac. TUNICATA 381 and directly continuous with that layer through the atrialaperture (fig. 6); consequently the mantle is covered both,^ externally and internally by / * ,.ft» ectodermal cells. •vA/^i / There is no true body I [^ cavity or coelom in the mesoderm; and yet the Tuni-cata are Coelomata in theirstructure and affinities, al-though it is very doubtfulwhether the enterocoelewhich has been described inthe development is reallyfound. In any case thecoelom if formed is after-wards suppressed, and inthe adult is only representedby the pericardium and itsderivati\cs and the smallcavities of the renal and re-productive organs. The branchial aperture (mouth) leads into the bran- chial siphon (buccal cavity or W<:/^/.fioor. stomojlaeum). //ij? ^ this opens into the anterior end of a very large cavity (the branchial sac) which extends nearly to the posterior end of the body (see figs. 5 and 6). This branchial sac is Diagrammatic dissection an enlarged and modified. BranchialSac and ItsFig. 5 of A. menlula to show the , Atrial aperture,ir, Branchial Branchial , Dorsal Dorsal , ^, Mantle. Nerve ganglion. Oesophagus. Oesophageal aperture. Ovar>-. Peribranchial , , , , Vas deferens. ng. ov,pbr, ngl, Subneural gland. pharynx, and is thereforeproperly a part of the ali-mentary canal. The oeso-phagus opens from it far backon the dorsal edge (see below).The wall of the branchial sacis pierced by a large numberof vert ical si it s^t he st ig-mata—placed in numeroustransverse rows (secondary orsubdivided gill-slits). Theseslits place the branchial sacin communication with theperibranchial or atrial cavity,which lies outside it (fig. 6).Between the stigmata thewall of the branchial sac istraversed by blood-vessels,w
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
