98 MOLLUSCA. 



supplies the posterior end of the corresponding lobe of the mantle. 

 Smaller nerves go to the posterior adductor muscle and gills. 



3. With a razor or sharp scalpel make a median sagittal 

 section of the foot, extending it some distance into the visceral 

 mass. This will expose the pedal ganglia, that lie just anterior 

 to a loop of the intestine, and dorsal to the muscular portion 

 of the foot. The pedal ganglia are connected with each other 

 by a broad commissure and with the cerebral ganglia by connec- 

 tives. 



By careful dissection it is possible to trace the connectives 

 and many of the nerves. The razor clam, Ensis, is especially 

 favorable for dissections of the nervous system, as the ganglia, 

 connectives, and many important nerves lie very near the 

 surface and can be seen without cutting the tissues above them. 



Make a drawing, indicating the position of the ganglia. 



Digestive System. This may be traced by following a guarded 

 bristle that has been inserted into the mouth of a specimen that 

 has been killed in hot water (not boiling), or by very carefully 

 picking off the tissue from one side. The intestine where it 

 penetrates the heart has already been seen, and may easily be 

 followed to the anus. 



The general arrangement of the alimentary canal is well 

 shown by a median sagittal section of a preserved specimen. 



The brownish digestive gland, commonly called the "liver," 

 will be seen surrounding a portion of the stomach. 



The enlargement on the intestine just posterior to the peri- 

 cardium is of unknown function. In some forms a special 

 diverticulum from the stomach bears a transparent cylindrical 

 rod, the crystalline style. This can easily be found in Mya. 

 Probably all lamellibranchs have similar structures more or less 

 well developed, but many do not have special pouches for their 

 formation. 



Draw the alimentary canal. (This may be included with 

 your sketch of the nervous system.) 



Cut a preserved specimen into transverse sections about a 

 quarter of an inch thick, and place the sections in their proper 



