70 THE GASTROPODA 



forms the posterior extremity of the foot bears a pair of tentacles 

 which are sometimes bifurcated, and in Phos there is a single filament 

 in this position. In Pterotrachea the foot terminates posteriorly in 

 a long filiform contractile appendage, bearing several annular vari- 

 cosities. In Cymbulia the posterior lobe of the foot also ends in a 

 long whip-like appendage. (6) On the sides of the foot, at about 

 the middle of its height, there is often a ridge, the epipodium, 

 extending from the head to the posterior end of the foot. This 

 ridge is specially well developed in various Rhipidoglossa (Fig. 1 30, 

 VIII), and may bear appendages of greater or less length, sensory 

 organs, and pigment spots, the last-named, however, showing no 

 trace of the structure of eyes. The anterior part of the epipodium 



Fio. 46. 



Rostellaria rectirostris, animal and shell, right-side view, a, snout or rostrum ; 1>, cephalic 

 tentacle ; c, eye ; d, anterior part of the foot ; e, posterior (operculigerous) part of the foot ; /, 

 operculum ; h', anterior canal of the shell, occupied by the pallial siphon. (From Lankester, 

 after Adams.) 



generally forms a cervical lobe, which exhibits a characteristic 

 asymmetry in certain Trochidae. The epipodium is found also 

 in Litiopa, the Rissoidae, Narica y Janthina, etc., and a portion of 

 it is represented by the cervical lobes in Paludim, Ampullaria, 

 and Calyptraea. 



The surface of the foot is normally furnished with a large number 

 of unicellular mucous glands, and very often these cells are specially 

 accumulated in invaginations of the integument, distinguished as 

 pedal glands. The most important of these invaginations are (1) 

 The anterior groove of the foot (Fig. 144, IV), into which open the 

 so-called labial glands : it is often continued into a fairly long canal. 

 This anterior pedal gland is very generally present in the aquatic 

 creeping species of Streptoneura and Opisthobranchs ; it secretes 

 the mucus which lubricates the surface of the foot, and is auxiliary 

 to creeping whether it be on the bottom ot the sea or on the 



