1895.] ANATOMY OJ? NAUTILUS POMPILIUS. 671 



As a matter of fact, however, such a viscero-pericardial aperture 

 is 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 sex \ 

 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 mm. 



It appears to me that there can be no question as to the homo- 

 logy of the tvi'o sets of apertures. In the genital segment, how- 

 ever, the migration of the ccelomic aperture has gone a little 

 further heyond the bounds of the kidney-sac. Each ccelomic 

 duct, plus its kidney-sac, \\ould on this view coiTespond to an 

 ordinary " nephridium," i. e., a tube leading from the ccelom to the 

 exterior, part of the wall of which has taken on an excretory 

 function. In the Dibi'anchs, in correlation with the disappear- 

 ance of the anterior gill, the corresponding kidney-sac has 

 disappeared, while its ccelomic duct persists as the genital duct. 

 The genital ducts of the Cephalopoda in general then are 

 nephridia ^, 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. On 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 onli/ the genital duct, or the 

 genital duct together with the genital gland of the same side ^ 



From the large ccelomic 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 some- 

 what elliptical in outline when seen from the anterior (dorsal) or 

 posterior (ventral) aspect (PL XXXIX. 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. 



' 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. 



^ Pelseneer asserts that the genital ducts of Cephalopods are nephridia — 

 without, however, qualifying his statement or supporting it by evidence. 



^ That it represents only the duct appears to me to be shown by the con- 

 dition in the very young animal, in which the inner part of the genital duct has 

 exactly the appearsvnce of the pyriform sac in the adult — the rudiment of the 

 gonad being quite distinct and apparently median and unpaired. 



