THE LAMELLIBRANCHIA 



221 



in adult forms, viz. three in certain Nuculidae, in Chama, and 

 Spondylus ; four in Area ; five in Pectunculus, Philobrya, and Pecten ; 

 and as many as twelve in Mytilus. The lumen of the hepatic 

 glands may be of considerable size, and form part of the digestive 

 and absorptive cavity. In certain Lucinidae (Montacuta, Axinus, 

 Fig. 238) the hepatic glands, together with the overlying gonads, 

 project into the pallial cavity in the form of arborescent tufts. 



The intestine almost always arises from the ventral side of the 

 stomach, and is sometimes provided with a valve at its origin 

 (Pinna). It is short and rectilinear or scarcely coiled in Solenomya, 

 in sundry Filibranchia such as Area, Pectunculus, Limopsis, Philobrya 

 (Fig. 234), Anomia, and in the Septibranchia (Fig. 251, in) ; but 



cu, 



cot 



FIG. 201. 



Median sagittal section of the anterior part of tho digestive tract of Donax. a.l, anterior 

 lip ; cae, caecum ; cr.s, crystalline style ; ctt, stomachal cuticle ; in, intestine ; m, mouth ; 

 oe, oesophagus ; p.l, posterior lip ; st, stomach. (After Uarrois.) 



more usually, as the Lammellibranchs are nearly all herbivorous, it 

 describes a certain number of convolutions in the viscero-pedal mass 

 (Fig. 242, al). These may vary from one to a dozen in number, 

 and sometimes they are confined to one side of the body ; in the 

 Nuculidae and Ledidae, for example, they are on the right side. 

 The intestine is ciliated throughout its whole length, and its rectal 

 portion is generally provided with an internal longitudinal ridge. 

 In Nucula (Fig. 204, XIV), Area, and Anomia the rectum passes 

 ventrad of the ventricle of the heart, as it does in Amphineura ; 

 but it traverses the ventricle, in rhipidoglossate fashion, in the 

 majority of Lammellibranchia. But in Malletia, Avicula, most 

 species of Ostraea, Miilleria, and Teredo (Fig. 195) it is dorsad 

 of the heart. Finally, the rectum always passes over the dorsal 

 side of the posterior adductor muscle, and ends behind it in 



