. Natural history. Geology; Zoology; Botany. ANATOMY OF CEPHALODISCUS NIGEESCENS. 39 seen passing backward obliquely to complete their course along the septum between the right and left collar cavities (text-fig. 10, mu. Ic). The gill-slit slopes from the pharyngeal cavity ventro-laterally and in the transverse plane. The collar canal slopes from the collar cavity dorso-laterally, and slightly backward. The external opening of the collar canal is more dorsal than that of the gill-slit, and a little more anterior. The gill-slit is such a short distance behind the collar canal that only occasion
. Natural history. Geology; Zoology; Botany. ANATOMY OF CEPHALODISCUS NIGEESCENS. 39 seen passing backward obliquely to complete their course along the septum between the right and left collar cavities (text-fig. 10, mu. Ic). The gill-slit slopes from the pharyngeal cavity ventro-laterally and in the transverse plane. The collar canal slopes from the collar cavity dorso-laterally, and slightly backward. The external opening of the collar canal is more dorsal than that of the gill-slit, and a little more anterior. The gill-slit is such a short distance behind the collar canal that only occasionally, as is shown on the right side of the text-fig. 14, is the canal wall missed entirely; more usually. Tbxt-Fig0be 14.—Section of a polypida of Cephalodiscus nigrescens taken transversely to the length of the body, and a little farther back than that shown in text-fig. 13. It passes through the gill-slits, and immediately behind the mouth. = thickened ventral V7all of the buccal shield; = part of the posterior wall of the collar canal cut tangentially ; = ooUar coelom ; = gastric diverticulum ; go. = gonad ; = gill-slit; i. = intestine ; ph. = dorsal wall of pharynx; pi. = pleurochord; — postero-lateral flap of the post-oral lamella bent over towards the mouth; , = muscle (see next); = longitudinal nerve tract; = subepidermal tissue behind the mouth, cut tangentially; = trunk coelom. the tangential section of the external part of the canal wall is included (text-fig. 14, c. ca.). As in the previous figure, the trunk cavity is conspicuous, and is occupied, at this particular level of section, by the two gonads, the intestine and the anterior. 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 National Antarctic Expedition, 1907-1904; Fletcher
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