. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. INTERNAL ANATOMY. 25 anastomosing of the branch- es, etc. It is essentially a median ventral outgrowth from the intestine, and its lying on one side of the pharynx in Amphioxus is only a secondary topographi- cal necessity.* Attached to the lateral muscular body-wall on each side are the gonadic pouches, which project into the cavity of the atrium. (Cf. Fig. 2.) Their number, which is usu- ally twenty-six pairs, varies slightly, and sometimes there are more on one side than on the other, as in Fig. 9. The at
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. INTERNAL ANATOMY. 25 anastomosing of the branch- es, etc. It is essentially a median ventral outgrowth from the intestine, and its lying on one side of the pharynx in Amphioxus is only a secondary topographi- cal necessity.* Attached to the lateral muscular body-wall on each side are the gonadic pouches, which project into the cavity of the atrium. (Cf. Fig. 2.) Their number, which is usu- ally twenty-six pairs, varies slightly, and sometimes there are more on one side than on the other, as in Fig. 9. The atrial cavity does not end at the atriopore, but is continued beyond it as a blind sac lying to the right of the intestine, and reach- ing back nearly as far as the Fig- 9- —Amphioxus dissected fiom T _. . the ventral side. (After Rathke, slightly anus. In l^lg. 9 the position altered.) of this pOSt-atrioPoml exten- . "': E"fance to mouth with the buccal ^ ^ cirn lying over it. p. c. Endo- SlOn of the atrium is indi- style. /. Hepatic co^cum. i;. Gonadic , 1 r 1 1 pouches, at. Position of atriopore; the Catecl by means Ot a dotted post-atrioporal extension of the atrium is ]|j^g indicated by the dotted line passing over to the right side of i, the intestine, an. Finally, in Fig. 9, the anus Anus. 1 . , ,,, — Note absence of differentiated is seen lying to the left of stomach. * The crecum is held in position by cord-like attachments to the ligamen- tum Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-. New York, London, Macmillan
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