19 



which extends therefore from gill to rectum. The 

 gland is made up of a number of deep lamellar foldings 

 of the mantle, about twenty in number. The structure 

 of this organ is considered elsewhere. 



The Anus (fig. 8) is situated at the apex of a 

 prominent papilla on the right side (topographical). 



The vaginal portion of the oviduct is conspicuous in 

 ripe females as an opaque white cylinder on the extreme 

 right. Its opening into the pallial cavity is not so 

 prominent as the anal opening by reason of the lowness 

 of the papilla. In male specimens the pallial cavity will 

 be filled by the large penis which usually lies twisted 

 backwards. All these organs terminate about the same 

 distance from the mantle edge and thus leave free a wide 

 region, the inner surface of the thickened margin. 



The Renal opening is a slit-like pore, situated to the 

 left of, and slightly above the rectum on the posterior wall 

 of the mantle cavity, in fact on the membrane separating 

 this cavity from the renal organ. The long axis of the 

 slit is dorso-ventral in direction. 



The Mantle Edge. 



A great part of the mantle, whether at the thickened 

 edge or in the region of the ctenidium and other organs of 

 the pallial complex, is composed of a modified connective 

 tissue. One sees in sections practically nothing but thin 

 cell walls with nuclei adhering to them, and here and 

 there fragments of muscle fibres. This characteristic 

 mantle connective tissue (figs. 31, x con. and 45, Fall, gl.) 

 is seen very well in the thickened edge, where it 

 occupies about | of the total thickness. Against the 

 epithelial layer, which bounds the surface of the mantle, 

 and underlying this everywhere, is a thick sheet of 

 compact fibrillar connective tissue of the more normal 



