The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . pointed out, by meansof a narrow duct with the front ofthe branchial sac (pharynx). Theopening of the duct is enlarged tolatm a funnel-shaped cavity, whichmay be folded upon itself, convoluted, ,or even broken up into a number of A Dorsal smaller openings, so as to form a ff tubercle, complicated projection, called the I,;dorsal tubercle, situated in the dorsal tjip^rt of the p
The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . pointed out, by meansof a narrow duct with the front ofthe branchial sac (pharynx). Theopening of the duct is enlarged tolatm a funnel-shaped cavity, whichmay be folded upon itself, convoluted, ,or even broken up into a number of A Dorsal smaller openings, so as to form a ff tubercle, complicated projection, called the I,;dorsal tubercle, situated in the dorsal tjip^rt of the prebranchial zone (fig. 7). mThe dorsal, tubercle in A. mentula issomewhat horse-shoe-shaped (fig. 8) ;it varies in form in most Ascidiansaccording to the genus and species,and in. some cases in the individualalso. Possibly, besides being the fio,opening of the duct from the sub-neural gland, it may be a sense-organfor testing the quality of the waterentering the branchial sac. Nervous. The single elongated ganglion in system. tJjg median dorsal line of the mantlebetween the branchial and atrial si-phons is the only nerve-centre in A. ?mentula and most otherTunicaia. It is the degenerate remains of the anterior. 7.— Diagrammatic sec-tion through auterior part of A. mentula,showing the relations ofthe nerve ganglion, -sob-neural glantl, &c. Letter-ing as for fig. 4; n, nerve ;n\ myelon ; ppt band; egl, gub^neural gland; sgd, itsdjict; C, test lining branch-Ul siphon. (Original.)
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Keywords: ., bookcentury1800, bookdecade1890, bookidencyclopedia, bookyear1892
