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 . 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.). Fio. 8.—Dorsal tuberrle ajil neighbouring organs of A. merUuIa. Lettering&3 before-;


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 . 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.). Fio. 8.—Dorsal tuberrle ajil neighbouring organs of A. merUuIa. Lettering&3 before-; egr, epibranchial groove, z, prsbranchial zone. (Original.) part of the cerebro-spinal nervous system of the tailedlarval Ascidian (see below, p. G14). The posterior orspinal part has entirely disappeared in most pprsists, however, in the Appendicutariidse, and traces ofit are found in some Ascidians (, Clavelina ; see Julin).The ganglion gives off distributory nerves at both ends, albo Herdman, Nature: vol. xxviii. p. 284. which run through the mantle to the neighbourh I^d of the Senseapertures, where they divide and subdivide. The only organs,sense-organs are the pigment spots between the branchialand atrial lobes, the tentacles at the base of the branchialsiphon, and possibly the dorsal tubercle and the languetsor dorsal lamina. These are all in a lowly developed con-dition. The larval Ascidians on the other hand have well-developed intra-cerebral optic and auditory sense-orga


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