ON THE ANATOMY OF NAUTILUS POMPILIUS. 185 



excretory and the genital organs as forming all parts of the 

 same organic complex. On reference to the diagrammatic 

 longitudinal section through the animal, it is seen that the 

 coelom is limited to the aboral end of the body, where it forms 

 a flattened space immediately undei'lying the body-wall — 

 between this latter and the thin membranous bag which limits 

 the cavity of the hsemocoel. The coelomic cavity is divided by 

 an oblique septum into a large upper division (^'.c), the genital 

 division of the coelom, and a smaller lower pericardium {p.c). 

 The septum separating these is not quite complete, being 

 perforated by three apertures of considerable size. One of 

 these is indicated in the diagram at a. 



The Genital division of the Coelom (g.c.) is, as already men- 

 tioned, the larger of the two coelomic chambers. It occupies 

 the extreme aboral (dorsal) end of the body, and is lined 

 throughout by a delicate epithelium composed of flattened 

 plate-like cells usually hexagonal in outline, the cell-boundaries, 

 however, being very indistinct. Each cell contains a rounded 

 nucleus with chromatin network and one or two small nucleoli. 

 Into this division of the coelom project the gizzard, the greater 

 part of the length of the intestine, and the genital gland. It 

 must of course be remembered that all these organs are 

 invested by the coelomic epithelium, so that it is only in a 

 certain sense that they can be said to be situated within the 

 cavity. The genital gland being merely a specialised part of 

 the wall of the coelom, it may appropriately be shortly described 

 at this point. 



The Ovary is a flattened ellipsoidal body attached by a 

 mesovarium to the lower (posterior) side of the intestine, and 

 at its oral (ventral) end having a considerable aperture which 

 throws its cavity into continuity with that of the surrounding 

 coelom. The general characters of the ovary are shown in 

 fig. 2, representing a sagittal section through the organ of an 

 immature female. The ovary exists here in almost its simplest 

 possible condition, in the form of a specialized ovigerous area of 

 the coelomic epithelium roofed over and protected by a simple 

 upgrowth from the coelomic wall. The outer surface of the 



