. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 228 77/A ASCIDIAXS. surface-view, but they are situated at the inner or con- cave sides of the two thickenings. On either side of the latter can be seen the ordinary cavity of the pharynx proceeding to- wards the oesophagus. At a later stage the openings of the two first-formed stigmata become distinctly visi- ble (Fig. iOSC). Mean- while a change of axis is taking place in the body of the young Ascidian. During the extraor- dinary change of axis
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 228 77/A ASCIDIAXS. surface-view, but they are situated at the inner or con- cave sides of the two thickenings. On either side of the latter can be seen the ordinary cavity of the pharynx proceeding to- wards the oesophagus. At a later stage the openings of the two first-formed stigmata become distinctly visi- ble (Fig. iOSC). Mean- while a change of axis is taking place in the body of the young Ascidian. During the extraor- dinary change of axis which we are about to describe the probos- ciform praeoral lobe (snout, organ of fixa- tion) remains station- ary, and the rest of the body actually rotates through an angle of go. i !i' illlj Fig. 107. â Young Cio}ia inteatinalis after the completion of the change of axis; from the left side. (After Wl ) /, IV\ Primary stigmata, a. Anus, situated . , immediately below the left atrial aperture, end. dCgrCCS, USmg the Or- Enddstyle. f. Organ of fixation. ^1^. Ganglion, cran of fixition aS 1. hy. Hypophysis. /;//. Intestine. Left atrial '^ a])erture. Longitudinal muscle, in. Mouth, pivot about which it oes, U'Lsophagus. Perijiharyngeal band. T TT" r py. Pyloric gland, st. Stomach. /. Coronary t^rUS. In rig. IO5 (. tentacles, Visceral nerve (cordon ganglion- \\^P rotation which naire visceral). takes place very gradu- ally is only half performed; while in Fig. 107 it is complete. The method of growth by which this rotation takes place hu I^^^ â ' *. 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, 1867-1942. New York; London : Mcmillan
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
