190 J. GRAHAM KERR. 



actual animal, however, one of these has become closed intern- 

 ally, 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 ccelomic opening to 

 the inner end of Needham's sac. 



On pulling the mantle dorsal wards, 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 men- 

 tioned, 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 Spirilla and .^Egopsids, 

 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 (Grobben, Lankester), an 

 identical process to that which has taken place in, e.g., the 

 geni to-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). 



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

 aperture is present, corresponding to the anterior kidney-open- 

 ing. 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 



^ 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. 



