35 



is quite near this point (figs. 17 and 18). In size the 

 stomach is rather less than the crop, and like the 

 oesophagus is lined by an easily detachable layer of chitin. 

 This lining is specially thick where it covers the grinding 

 pads (figs. 18 and 19, ch ± , pad.). Where it covers the 

 posterior wall of the stomach, however, it is smooth and 

 thin. At the exit of the spiral caecum and intestine the 

 cuticle ends, thus leaving a circular orifice through which 

 food passes onwards from the stomach (PL V, fig. 38, or.). 

 The food is ground in the stomach, and also well mixed 

 up with the digestive fluid which enters from the spiral 

 caecum (Bourquelot), so that here digestion takes place. 



Spiral Caecum.— A narrow passage leading out from 

 the stomach, soon bifurcates, and so gives rise to the spiral 

 caecum on the one hand and the intestine on the other 

 (PL V, fig. 38, Int. ap.). 



The spiral caecum is in reality a long narrow sac, 

 e.g., caecum in Lofigo, which in the Octopodidae and 

 others becomes curled in a spiral of one and a half turns. 

 It is thin walled, and the internal sej)ta are seen faintly 

 from outside (PL IV, fig. 28). The columella of the spiral 

 is on the side opposite to the intestine (fig. 38). On 

 cutting open the caecum along the columellar edge, and 

 pinning it out, it will be seen that there is a series of 

 delicate folded valves, running transversely to its length 

 (fig. 38, v., Vj). Cuvier described a spiral valve running 

 down the caecum in Octopus, but in Eledone there is a 

 series of short transverse valves instead, closely set. They 

 are widest centrally, and taper at their two ends, which 

 are attached to the columellar region of the wall. Along 

 this columellar region also runs a longitudinal fold, at 

 the side of which enters the common hepatic duct, some 

 distance from the anterior end of the caecum (fig. 38, 

 h. a p.). Probably this fold guides the digestive secretion 



