ON THE ANATOMY OF NAUTILUS POMPILIUS. 189 



blood-sinuses. Between the lobules these are greatly developed, 

 their separation walls being reduced to fine connective tissue- 

 threads serving to bind the lobes together. Into the substance 

 of the lobules also pass continuations of the sinuses. Regarding 

 the character of the epithelium in different parts of the tubes, 

 the state of the specimens does not allow me to say anything. 



The Pericardium or inferior chamber of the coelom is con- 

 siderably smaller than that already described. It immediately 

 underlies the " postero-dorsal " body-wall throughout its half 

 next the mantle-flap, and its cavity is conveniently exposed by 

 reflection of its external wall. It is then seen to be quad- 

 rangular in outline, rather broader than long (68 mm. x 54 mm. 

 in one specimen). From its inner (anterior) wall, in a curved 

 row parallel to the 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 frasnum, 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 — the 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 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 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 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-peiicardial aperture. The genital 

 division of the coelom primitively possesses at its ventral end 

 also a communication upon each side with the exterior. In the 

 VOL. VL 17 



