284 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



the pericardium ; it then passes through the glandular 

 walls of the renal organs to the gills, and is then returned 

 to the auricles, to be again driven to the various organs of 

 the body. 



p. The Digestive Organs. It is very difficult to trace 

 these in a fresh specimen, and one which has been hard- 

 ened in alcohol should therefore be used. 



1. Notice the mouth, on the middle line of the body, 

 under the anterior adductor muscle, and between the labial 

 palpi. 



2. Carefully dissect it out and trace it upwards to the 

 small, irregular stomach. 



3. Around the stomach notice the compact, dark, brown 

 liver, which opens, by several irregular apertures, into the 

 stomach. 



4. The intestine is a long, delicate tube, which is em- 

 bedded in the light-colored reproductive organs, which 

 form the greater part of the abdomen. It first runs 

 downwards from the stomach nearly to the foot ; then 

 upwards nearly to the dorsal surface ; then down again 

 nearly to the foot, where it bends forwards and then up- 

 wards to leave the abdomen and enter the pericardium. 

 It passes through the ventricle, and, leaving the pericar- 

 dium at its posterior end, passes over the posterior adduc- 

 tor muscle. 



5. The posterior end of the intestine, or the rectum, 

 bends around the adductor muscle, to open at the anus 

 into the cloaca! chamber, close to its aperture, so that the 

 faeces are swept out of the mantle cavity by the current 

 of water from the gills. 



q. The reproductive organs. These make up the greater 

 part of the substance of the abdomen, and are alike in 

 form in both sexes. They vary in size with the season, 



