THE FRESH- WATER MUSSEL. 



103 



yourself, put a fresh unopened mussel with, the small 

 end upward into a tumbler of water containing a little 

 indigo, and the blue grains will show you the direction 

 of the current. You can see the grains go in at the 

 large and out at the small end (Fig. 98). I have spoken 



Fig. 98. 



Back-Door, or Dorsal 

 Siphon. 



Front-Door, or Ventral Siphon. 



Clam, or Mussel, in a Vessel of Indigo Water.— The Arrows point the Di- 

 rection of the Current, as seen by the Grains of Indigo. 



of the h^art, through which the intestine passes. In 

 order to see the heart well, you must get a fresh mussel 

 and lift him entirely out of his shell ; but, before you 

 can do this, you must cut all the straps, then, if you 



