ELEDONE. 489 
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; Pl. Il, fig. 8; ,). 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 
