670 ME. .1. GEAHAM KEEB 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 fr£enum, which 

 on each side connects the anterior wall of the 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 coelom, 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 pericar- 

 dium. 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 coelom 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 frsenum 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 tbe 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. 



On 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 openmgs, one sees the slit-like viscero-pericardial aper- 

 tures, 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 Sjpirula and -Sgopsids, 

 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 (Grrobben, 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 forma- 

 tion — 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). 



