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Show 1895.] ANATOMY OP NAUTILUS POMPILIUS. 671 • As a matter of fact, however, such a viscero-pericardial aperture iff present, corresponding to the anterior kidney-opening. It is the primitive genital aperture. Such is seen either in the case of the oviduct or of the rudimentary left genital duct of either sexl. This opening leads into the genital division of the ccelom just as does the viscero-pericardial pore into the pericardium, and, like it, is situated mesiad to the kidney-opening. The only striking difference is, that this pore is normally rather farther apart from its corresponding kidney-opening than is the viscero-pericardial pore. The latter is normally quite close to its kidney-opening, but its distance from it is very variable and may reach 3 m m . It appears to m e that there can be no question as to the homology of the two sets of apertures. In the genital segment, however, the migration of the coelomic aperture has gone a little further beyond the bounds of the kidney-sac. Each ccelomic duct, plus its kidney-sac, would on this view correspond to an ordinary " nephridium," i. e., a tube leading from the coelom to the exterior, part of the wall of which has taken on an excretory function. In the Dibranchs, in correlation with the disappearance of the anterior gill, the corresponding kidney-sac has disappeared, while its coelomic duct persists as the genital duct. Tbe genital ducts of the Cephalopoda in general then are nephridia2, minus their excretory sacs. III. The Male Genital Ducts and Penis. The general disposition of the genital apparatus in the male is shown in fig. 3 (p. 672). As is well known, only the duct of the right side is functional in Nautilus. O n the left side there is the "pyriform sac" of Owen, shown by Lankester and Bourne to represent the left genital duct, although the question was left open by them-whether it represented only the genital duct, or the genital duct together with the genital gland of the same side3. From the large coelomic aperture the genital duct passes through the quadrangular " accessory gland " composed of numerous caecal tubular outgrowths from the duct itself. Beyond this point the duct opens into the spermatophore sac-a large structure somewhat elliptical in outline when seen from the anterior (dorsal) or posterior (ventral) aspect (PI. X X X I X . fig. 1). The vas deferens opens into this at its outer end. Internal to this opening there begins a longitudinal septum which divides the cavity of the sac through about half its length-terminating in a free concave edge. 1 In the case of the functional genital duct of the male, a shifting of the external aperture has taken place through the, in all probability, secondary development from the adjoining body-wall of the penis. 2 Pelseneer asserts that the genital ducts of Cephalopods are nephridia- without, however, qualifying his statement or supporting it by evidence. 3 That it represents only the duct appears to m e to be shown by the condition in the very young animal, in which the inner part of the genital duct has exactly tbe appearance of the pyriform sac in the adult-the rudiment of the gonad being quite distinct and apparently median and impaired. |