56 THE AMPHINEURA 



II. ANATOMY. 



Digestive Tract. The mouth is anterior and ventral, and is 

 frequently sm-rounded by papillae, probably sensory in function. 

 It opens into a muscular and sometimes protractile pharynx lined 

 by a thick cuticle. The salivary glands and radular sac open into 

 the pharynx. The radula (Fig. 36), when present, comprises several 

 rows of teeth, and may be (1) polystichous, with a continuous line 

 of teeth in each row (Proneomenia and Macellomenia}, in which case 

 a basal membrane may be present, forming a true continuous 

 polyserial radula (Proneomenia acuminata, P. sluiten, P. gerlachei), or 

 absent, forming a discontinuous polyserial radula (P. vagans) ; (2) 

 distichous, with two separate teeth (Paramenia, Pararhopalia, Ismcnia, 



B 



FIG. 



Radula (transverse rows) of various Neo- 

 meniomorpha. A, Proneomenia (Hubrecht) ; 



CB, Lepidainenia (Kowalewsky and Marion) ; 

 V/UUU/Jd C, Macellomenia (Pruvot); D, Amphimenia 



( -J (Thiele) ; E, Stylomenia (Pruvot). 



Lepidomenia, Dinomenia] ; (3) monostichous, with a single tooth 

 (Stylomenia, Dondersia, Amphimenia, Proparamenia). The radula is 

 entirely absent in the Neomeniidae, in fihopalomenia, Prurotia, 

 Strophomenia, and Notomenia. 



The salivary glands form a symmetrical pair, lying on the 

 ventral side, and opening on .a subradular prominence ; their ducts 

 sometimes unite before opening into the pharynx. They correspond 

 to the subradular glands of the Polyplacophora and the posterior 

 salivary glands of the Cephalopoda. In some forms there is a 

 second pair of salivary glands, dorsal or dorso-lateral in position, 

 opening by a single duct into the mid-pharynx (Paramenia, some 

 species of Proneomenia: Fig. 37, gl.s.d). Several genera, among 

 them Neomenia, are devoid of salivary glands. The oesophagus is 

 generally short, and leads into a cylindrical and rectilinear stomach, 

 which frequently sends forward a caecum dorsad of the oesophagus, 

 and is provided with symmetrical lateral caeca, giving to the organ 

 the appearance of regular segmentation. The whole surface of the 



