26 



oilier Decapods, and this means of locking the mantle 

 seems to have weakened as the dorsal fusion formed, and 

 so rendered it less necessary. Also, as Eledone is a much 

 less powerful swimmer than the Decapods, the need of a 

 strong funnel articulation is lessened. The funnel cavity 

 is three-chambered. The central largest chamber alone 

 opens to the exterior, while the lateral chambers are blind 

 anteriorly. All three, however, open into the mantle 

 cavity. The central chamber is cut off laterally from the 

 side chambers by the great depressor or retractor muscle 

 of the funnel. This forms the ventral and ventro-lateral 

 wall of ils own side of the funnel, and then runs out to 

 its insertion on the anterior border of the mantle cartilage 

 of its side. Two other pairs of muscular bands, which 

 are narrow and rather short, run in from the dorsal 

 surface of the funnel to the cephalopedal mass. They 

 act as protractors of the funnel, and are exposed by 

 cutting through the skin behind the funnel, as in PI. II, 

 fig. 9, sle., and turning the funnel ventrally. The 

 protractors form a letter W, the external pair being 

 inserted above the inner pair, on the funnel wall. The 

 external pair run outwards and dorsally, to join in with 

 the capito-pedal muscles just below the eyes. The 

 internal pair run inwards to the ventral surface of the 

 cranial cartilage, and are attached there. The dorsal wall 

 of the funnel is formed by a broad pair of muscles which 

 then run outwards from the posterior lateral region of the 

 funnel to the top of the mantle. Thus with the depressor, 

 these two nuchal or collar muscles bound the lateral 

 tunnel chamber. Hence the funnel muscles are arranged 

 in three sets : 



(a) One pair of depressors (tig. 9a,, F.I).), 



(h) One pair of nuchal muscles (tig. 9, coll.), and 



(<■) Two pairs of protractors (fig. 9, L.F.Pr., L.F.Pi\). 



