21 



Mantle. 



The mantle encloses the visceral mass, forming a sac 

 with thick muscular walls, which extends from the 

 posterior end of the body as far as the posterior border 

 of the head dorsally and of the funnel ventrally (PI. I, 

 fig. 1 ; PI. II, fig. 8 ; Mj). Morphologically it is an out- 

 growth of the posterior part of the visceral envelope, and 

 hence its inner wall is continuous with the outer wall of 

 the visceral sac. The space between these two walls is 

 the mantle cavity. The anterior edge of this sac is fused 

 with the head dorsally, but ventrally and laterally it is 

 free, so that a wide entrance to the mantle cavity is thus 

 left. 



The Mantle Cavity may best be studied by cutting 

 the mantle down from the free edge on each side 

 of the mid ventral line, so as to expose the organs 

 contained therein. It is a deep cavity, as in Sepia 

 and most Cephalopods, and is more spacious ventrally 

 and laterally than dorsally, in order to enclose the 

 important pallial complex. The body is bound to the 

 enveloping mantle by: — (1) The above-mentioned dorsal 

 fusion of head and mantle : (2) the shallow siphono-pallial 

 articulation; (3) a vertical muscular septum running out 

 from the median ventral line of the inner surface of the 

 mantle to the visceral mass and dividing the mantle cavity 

 into symmetrical halves; (4) the posterior continuity of 

 the inner surface of the mantle with the external 

 epithelium of the visceral mass; (5) two pairs of 

 muscular bands running out from the afferent and efferent 

 axes respectively of the gills the band running along the 

 outer surface of the efferent vessel is inserted on the inner 

 ventral surface of the mantle, posterior to the insertion of 

 the vertical septum, and that running along the inner 



