58 



leaving this vessel at the base of the gill, is continued in 

 towards its fellow over the ventral side of the viscera] 

 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 (PI. V, tig'. 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. 51), 

 Br.gld.). 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 beariug 

 the aerating filaments on their outer surface (PI. 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, i.e. the 

 supporting pillars on the external side of the gill 

 alternate with those on the internal surface. Counting 



