. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 20 ANATOMY OF AMPHIOXUS. guarded against the intrusion of noxious substances. Everything entering the mouth has to pass through a vestibule richly provided with sensitive epithehal cells. This vestibule consists of the oral hood with its marginal cirri, at the back of which lies the definite oral opening or velum, as it was called by Huxley on account of its resemblance to a similar structure in the young lamprey (Ammocoetes). (Cf. Fig. 3.) In the adult the velum carries twelve tentacles of its own, the vela
. Amphioxus and the ancestry of the vertebrates. Amphioxus; Sea squirts; Hemichordata. 20 ANATOMY OF AMPHIOXUS. guarded against the intrusion of noxious substances. Everything entering the mouth has to pass through a vestibule richly provided with sensitive epithehal cells. This vestibule consists of the oral hood with its marginal cirri, at the back of which lies the definite oral opening or velum, as it was called by Huxley on account of its resemblance to a similar structure in the young lamprey (Ammocoetes). (Cf. Fig. 3.) In the adult the velum carries twelve tentacles of its own, the velar tentacles, which are not to be confused with the buccal cirri of the oral hood. The velar tentacles project in a backward direction freely into the Fig. 6. —A. Portion of a buccal cirrus to show groups of sense-cells. B. Isolated cells of the skin ; two columnar sense-cells carrying a sensory hair and one cylindrical epidermic cell with striated cuticular border. (After Lan- GERHANS.) Groups of sense-cells occur on the side of the buccal cirri at intervals (Fig. 6). Some of these cells bear a vibratile cilium at their free ends, and others bear stiff hairs. Both kinds of cells are mingled in the same 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
Size: 1473px × 1696px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
