OCR Text |
Show 670 MR. J. GRAHAM KERR ON THE [June 18, ventral (oral) border of the chamber, project the four clusters of pericardial gland-follicles. The external pair are in such a view (i. e., from posterior) partially hidden by a broad fraenum, which on each side connects the anterior wall of tbe chamber with the posterior wall. Dorsal (aboral) to the two central pericardial glands is seen the ventricle firmly bound down to the anterior wall of the chamber-tbe epithelium lining which is reflected over its surface. Just dorsal to the ventricle a large rounded aperture leads into the genital division of the ccelom, and ventral to it is a still larger such opening. The four auricles attached to the corners of the ventricle, unlike it, hang quite free in the pericardium. In some specimens these were markedly asymmetrical, those of the left side being much more dilated than those of the right. Each of the divisions of the ccelom above described is in open communication with the exterior. In the case of the pericardium, one finds at its ventral end that the cavity is prolonged on either side on the anterior face of the fraenum mentioned. Each such prolongation forms a small somewhat triangular chamber with its greatest diameter transverse, and this at its mesiad end opens into the mantle-cavity by the tumid lipped, so-called viscero-pericardial aperture. The genital division of the coelom primitively possesses at its ventral end also a communication upon each side with the exterior. In the actual animal, however, one of these has become closed internally, as Lankester has shown, while the other persists in the female as the oviduct, in the male probably as the part of the functional genital duct extending from its coelomic opening to the inner end of Needham's sac. O n pulling the mantle dorsalwards, so as to afford a view of the interior of the mantle-cavity, such as that shown in Lankester and Bourne's figure, one notices a little distance to the headward side of the root of each gill one of the four kidney-openings. These are arranged in two pairs. Just to the mesiad side of each of the posterior openings, one sees the slit-like viscero-pericardial apertures, leading, as above mentioned, into the pericardium. This condition in Nautilus, where the viscero-pericardial sac opens independently of the kidney, is homologized, and no doubt rightly so, with the condition met with in Spirula and iEgopsids, where the viscero-pericardial canal opens into the kidney-sac near its mouth, by supposing the opening of the latter to have migrated on to the outer surface (Grobbeu, Lankester), an identical process to that which has taken place in, e. g., the genito-urinary passage and the rectum in Mammals. Accompanying the anterior kidney openings no such pericardio-visceral pores are seen, and in consequence of this it has been concluded that the anterior and posterior kidney-sacs are not serially homologous. All agree in regarding the posterior one as primitive, but the anterior sac is looked on as a secondary formation- either as a secondarily arising repetition of the posterior one, or as having been split off from it in correlation with the development of a new gill and new afferent vessel (Grobben). |