64 GENERAL BIOLOGY. 



2. The oesophagus ; a short straight tube ex- 



tending obliquely upward to : 



3. The stomach : a dilatation of the alimentary 



canal. 



(The intestine passes with many turns through 

 the visceral mass, and will be seen later in 

 sections.) 



In ike same way open the rectum frown the anus, 

 and trace its course through the pericardia! 

 cavity. 



Look for the typhlosole. 

 V. The Gills. 



1. Take out one of the gills, cut it transversely, 



and examine the cut edge with a hand-lens. 



2. Examine with the low and then with the high 



power a small piece of one lamella. 



3. In some specimens the outer gills are dis- 



tended with young mussels (glochidia). If 

 these can be obtained, mount and examine 

 with a low and with a high power. 

 C. Sections. 



Remove the shell from a second specimen, place 

 the mussel on its side upon the wax in a dis- 

 secting-pan, and with a razor make sections a 

 quarter of an inch thick. A.rrange the sections 

 in order, fastening each in place with a pin y 

 and cover them with water. 

 Study especially the following sections : 



