526 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
leaving this vessel at the base of the gill, is continued in 
towards its fellow over the ventral side of the visceral 
mass. ‘The second, running along the inner side of the 
afferent vessel from its tip, is inserted with the depressor 
infundibuli into the mantle, at the anterior end of the 
mantle cartilage of its side. ‘These two bands of muscle 
probably serve to deflect the gill, and also by their 
contraction help the circulation of blood in the vessel 
each respectively covers. (2) The afferent and efferent 
vessels, which are continued from the gill into the visceral 
mass, help to bind them. 
The septum which joins the mantle and gill together 
is triangular in shape. The apex of the triangle points 
posteriorly, and the base, which is the shortest side, 
anteriorly. This side is free, and allows the gill to be 
deflected laterally. That side of the triangle which joins 
on to the mantle is the longest (Pl. V, fig. 59, Br. mem.). 
The dorsal part of the septum is thin, membranous and 
transparent in a fresh specimen, but along the edge 
attached to the gill runs a broad fleshy band, the so-called 
* spleen,’ which lies dorsal to the afferent vessel (fig. 59, 
Br.gid.). During life the gills are exceedingly graceful 
objects, semi-transparent and colourless, and are deflected 
laterally to and fro in the mantle cavity. 
The structure of the gill is exceedingly complex, 
much more so than the gill of Sepia and other Decapods. 
The walls of the hollow gill cone are formed by pillars of 
connective tissue penetrated by blood vessels, and bearing 
the aerating filaments on their outer surface (Pl. V, fig. 
60). There are eleven to thirteen pairs of leaflets in 
Eledone, the number varying slightly with the size of the 
specimen. These are arranged in alternate pairs, 1.e. the 
supporting pillars on the external side of the gill 
alternate with those on the internal surface. Counting 
