MOLLUSCS. 759 



(Helix, Limax), or at the side of it two jaws are found. The 

 intestinal canal has various lengths, but is usually tortuous and 

 longer than the body ; it is very long, for instance, in Chiton and 

 Patella, and makes many convolutions which are straitly enclosed by 

 the liver. The oesophagus is sometimes expanded at the lower end 

 like a crop, as in Limnceus, Planorbis, Nautilus and Octopus, which 

 has longitudinal folds like those usually occurring in the oesopha- 

 gus. The stomach is in some, as in Helix, membranous, in others 

 muscular. In many this muscular stomach is armed internally 

 with hard parts, as in Scyllcea, Sulla, Bullcea, or the inner mem- 

 brane is horny, as in Tethys and the Cephalopoda, just as it is in 

 gallinaceous birds. There are often found pieces of Crustacea in this 

 stomach, whence it may be concluded that a hard covering of this 

 kind is serviceable for crushing hard food. In some the stomach 

 is compound, as in Onchidium and Aplysia, in which three (or 

 in the last named genus, according to CUVIER, even four) stomachs 

 are present. The first stomach is here membranous, the second 

 muscular, armed internally with larger cartilaginous teeth placed in 

 circles alternately, and with a single row of smaller teeth at the 

 upper edge ; the third stomach is armed on its inner surface with 

 hooks which are curved forwards ; the fourth, finally, is an elongated 

 blind sac, which is surrounded by the liver. According to OWEN, 

 this blind sac may be a secreting organ, a pancreas in the simplest 

 form, corresponding to the coecal appendages at the inferior orifice 

 of the stomach in fishes 1 . As such also he regards the so-called 

 second stomach in the Cephalopods, a membranous blind appendage 

 behind the muscular stomach, which in Sepia and Octopus incloses 

 a spiral membranous valve, and in Nautilus is parted into many 

 chambers by thin transverse membranous valves 2 . The termina- 

 tion of the rectum in molluscs is usually situated on the right 

 side of the body, always in the neighbourhood of the respiratory 

 organs. 



Salivary glands, which are wanting in the preceding class, 

 appear very constantly to be present in this. Commonly there are 



1 Lectures on the compar. Anat. of the invert. Anim. p. 300; sec. ed. p. 557. 



2 In some cephalopods there are folliculi, larger than the liver itself, which are 

 attached to the gall-ducts; HUNTER regarded these as pancreas (Physiol. Catalogue I. 

 p. 229), in which opinion V. SIEBOLD also participates. Lchrb. dcr vcrgl. Anat. 



s- 393- 



