APLYSIA. 211 



stomachs (Fig. 8, ant. giz. and p. giz.), and by those who call 

 the crop the first stomach, the second and third stomachs. 

 The lumen of both chambers is very small, for, in addition to 

 the thickness of the wall, the inner lining is beset with semi- 

 transparent horny teeth. These are probably of little use 

 for grinding purposes, but compress and strain the food so as 

 to prepare it for the action of the digestive juices. In the 

 first triturating stomach are from twelve to twenty teeth. 

 (Fig. 11, a. b.) These are large and stout, with diamond- 

 shaped bases set in sockets in the walls. They are readily 

 detachable. Their shape varies ; some are almost perfect 

 pyramids, others like the Cap of Liberty, with backwardly 

 directed points. Between the teeth the walls of the gizzard 

 are thrown into folds. In the second portion of the gizzard 

 the teeth are much more slender. (Fig. 11, c.) They are long 

 and tapering, with pointed tips and ovoid bases, and are about 

 twelve in number. 



Stomach and Caecum. At this point the alimentary canal 

 becomes embedded in the digestive gland. A pair of valves 

 (Fig. 12, I. stom. v.), muscular and covered with long vibratile 

 cilia, regulate the passage of the food from the posterior 

 portion of the gizzard into the morphological stomach. Up to 

 the present no change of a digestive nature has taken place 

 in the food, and in sections of the preceding portions of the 

 canal, the histological elements of the weed are plainly visible. 

 Digestion proper is initiated in the stomach (Fig. 8, stom.), 

 which forms an ill-defined chamber, the " camera biliare " of 

 Zuccardi. The stomach receives the discharge from the 

 " liver " by a variable number of ducts (usually three on the 

 right side and one on the left). The ducts are almost equal 

 in diameter to the stomach itself. They are strongly ciliated 

 so as to drive the hepatic fluid forwards into the alimentary 

 canal. It is probable that the bile is not only digestive but 

 also excretory. The liver is more properly an hepato-pancreas, 

 but functions also as an accessory kidney. 



