372 ORGANS OF DIGESTION. 



most of the higher mollusca, the organs of generation occupy 

 the posterior part of the abdominal cavity, especially the 

 ovary (121. s.) and the testicle (121. t.) with its convoluted 

 epididymis, but the common canal of both these organs ascends 

 on the right side to the penis (121. g.} near the head, 

 and the urinary sac (121 u.) opens into the same common 

 excretory passage. 



There are four gastric cavities in the pleurobranchus 

 of Peron, and the capacious stomach of the pleurobranchea 

 extends nearly the whole length of the body. Horny teeth 

 are found in the stomach of the tritonia, scylloea, and 

 most other phytophagous gasteropods; in place of teeth 

 the stomach of the tethys is lined with a firm coriaceous 

 epithelium ; and the sides of the muscular round stomach 

 of the bullos are provided with two dense rhomboidal horny 

 plates, with their convex surfaces directed inwards towards 

 each other to masticate the food. In the patella the tongue 

 is longer than the whole body, and is covered over with 

 regular transverse rows of sharp recurved spines for filing 

 down the coarse marine plants on which it subsists. The 

 oesophagus is wide and sacculated at its upper part, and 

 passes narrow through the liver nearly to the posterior 

 extremity of the body before entering the capacious transverse 

 stomach which has an elongated form with its orifices ter- 

 minal, and the intestine, long and convoluted through the 

 mass of a large liver, terminates in a slightly dilated rectum 

 which opens on the right side near the head. There are two 

 horny maxillae in the tritonia and scylloea, besides the usual 

 sharp spines on the surface of the tongue, and in the limnoea 

 and planorbis there is a superior dentated maxilla besides 

 the two ordinary lateral jaws. These maxillae are articulated 

 together; they are moved by powerful enveloping muscles, 

 and they are lateral in their position like those of articulated 

 animals. There is a superior dentated jaw in the snails for 

 reducing their vegetable food ; there are three gastric sacs in 

 the onchidium which are pli^ted longitudinally within, and 

 the biliary ducts here enter the oesophagus as well as the 

 stomach. The rectum opens on the right side in the naked 

 limaces, as in the testaceous helices, on the median line in 

 the testacella as in the doris, and on the left side in the 

 planorbis which has the apex of its suborbicular shell slightly 



