LIVER OF MOLLUSCA, 



365 



lu the Placopliora it forms a paii' of symmetrically disposed 

 branched tubes. 



lu the Gastropoda this gland is no less Avell developed. In the 

 shelled forms it occupies the largest portion of the visceral sac 

 within the shell ; it is always made up of a number of large lobes, 

 and embraces more or less of the enteron. The bile-ducts from the 

 lobes either open separately or together into the first portion of the 

 mid-srut, and sometimes also into the stomach-like enlaro:ement. 

 The numbei', as well as the relative size of the separate portions of 

 the liver, varies greatly. As a rule, however, when the liver increases 

 in size it becomes less complex, while the smaller the lobes the more 

 numerous they are. 



This mode of arrangement along a large portion of the enteric 

 canal leads to certain changes in this 

 portion of the enteron in one division of 

 the Opisthobranchiata. The ducts of the 

 several lobes of the liver widen out, and 

 so form diverticula of the stomach ; when, 

 therefore, there are a large number of 

 hepatic tubes opening into the stomach, 

 its inner surface has a reticular appear- 

 ance (Doris, Doridopsis). Owing to this 

 change, which is easily explicable by a 

 reference to the origin of the liver, the 

 glandular portion of this organ becomes 

 apparently a mere covering for these 

 irregular diverticula. 



This is indeed the origin of that 

 arrangement of the digestive system in 

 the JEolidifB and others, to which we 

 have already called attention (§ 278). 

 The liver has the form of wide ctecal 

 appendages, which arise from the mid- 

 gut (Fig. 194, m), or so-called stomach. 

 They are either directly connected, when 

 the appendages open at once into the 

 mid-gut, or indirectly, when they still 

 form wide diverticula of it (Fig. 1 94) ; 

 and these, too, may be due to certain 

 changes in a part of the liver. These appendages traverse the 

 coelom and send blind processes into the dorsal cirri, when such 

 are present. These processes are more or less branched, according 

 to the number present, and they may, further, anastomose with one 

 another. The size, just as much as the number and general form 

 of the enteric appendages, may vary. Sometimes they are mere 

 diverticula of the enteron, and may communicate with it by wide 

 openings, and even be large enough to take in masses of food ; or, 

 ao"ain, they may form narrow canals which do not take any direct 

 share in the reception of the food. There are intermediate stages 



Pig. 191. Enteric canal of 

 iBolidia papillosa. p/iPha- 

 rynx. m Mid-gut, with its he- 

 patic appendages, (h) all of 

 which are not figured, e Hind- 

 gut, art Anus (after Alder and 

 Hancock). 



