PHYSIOLOGY OF THE INVERTEBRATA. 69 



likely to mix the food particles with the secretions of the 

 stomach and those poured into it from the ducts of the large 

 digestive gland (" liver "), which surrounds the stomach. 

 The crystalline style is well-developed in Mya^ CytJierea, &c. ; 

 but in Ostrea it only exists in a rudimentary state as a piece 

 x)f cartilage ; and in Fholas it is said to have the form of a 

 folded plate. 



The Lamellibranch stomach leads into a long intestine, 

 which turns downwards and makes many convolutions among 

 the so-called liver and genital gland, and again comes into 

 the dorsal region, where it traverses the heart, leaving the 

 pericardium at its posterior end, and ultimately terminates in 

 an anus situated behind the posterior adductor muscle. The 

 anus is placed on a projecting papilla. That portion of the 

 intestine from where it enters the heart to the anal aperture 

 is usually called the rectum. In a transverse section, the 

 intestine is horseshoe-shaped, due to the folding in of its 

 dorsal wall, consequently forming a typhlosole.. The so-called 

 liver, which is pancreatio in function, consists of numerous 

 branched csecal follicles. These a,re united into ducts which 

 open into the stomach by several irregular apertures. There 

 are no salivary glands in the Lariiellibranchiata. 



(2) The ScapJwpoda. — In Dentalium the mouth is sur- 

 rounded by many filiform tentacala which play the rSle of 

 prehensile organs. The mouth leads into a buccal chamber 

 containing the odontophore — a prehensile rasp-like tongue. 

 The buccal chamber passes into the oesophagus leading into 

 the stomach. The intestine then follows, and , after being 

 coiled several times, terminates in an anus behind the root of 

 the foot. 



The intestine of the Scaphopoda does not traverse the heart, 

 as in the Lamellibranchiata, for that organ is entirely absent. 

 The so-called liver is bilobed. 



(3) The Polyplacophora are vermiform MoUu$ca without 

 eyes or tentacula. In Chiton the shell is unlike that of any 

 other Mollusc. It consists of eight calcified plates arra,nged. 



