FEESH-WATEE MUSSEL 197 



gill consists of two lamellss united by the par- 

 titions mentioned above, which are the inter- 

 lamellar junctions. Examine also with the low 

 power, and try to make out the oval inhalent 

 apertures opening on the face of the gill into 

 the water -tubes. Scrape the surface of a gill of 

 a living mussel, and examine the ciliated cells 

 thus set free. Examine a piece of a split gill of 

 a living mussel under the low power, and note the 

 ciliary action. Compare the gills with each 

 other as regards shape, size, color, structure, at- 

 tachment, etc. 

 Make drawings showing the gross and the minute 

 structure of a giU. 



Jc. The mouth. — "What is its position with regard to 

 foot, anterior adductor muscle, siphons, and gills ? 

 What is its shape ? Size ? Are there any jaws ? 

 Teeth ? A tongue ? "What kind of food can the 

 mussel eat ? 



I. The labial palpi. — "What is their position with re- 

 gard to the mouth and gills ? Number ? Shape ? 

 Color? Attachments? Compare with giUs as 

 regards shape, size, and structure. Are they at 

 all like the palpi seen on the lobster and locust ? 



m. The anus. — "What is its position? With which si- 

 phon is it connected ? 

 Make the following drawings : (1) A side view of the 

 mussel lying in one valve of the shell, to show the posi- 

 tion of the muscles, etc. ; (2) a side view with one man- 

 tle lobe turned back ; (3) a side view with mantle lobe 

 and gills turned back. 



