102 



BOYS AND GIRLS IN BIOLOGY. 



a windpipe, because it does not breathe air. The squar- 

 ish bag is the stomach, and at the back part of this you 

 can see the opening into a long, narrow tube, which is 

 the intestine. The intestine then leaves the stomach, 

 and runs down into the foot (Fig. 97), where it seems 

 to get bewildered, and after two turns passes out again, 

 and goes up to the dorsal edge of the body, runs right 

 through the heart straight back to the cloacal chamber, 

 where it ends by a small opening called the anus (Fig. 

 97). The stomach and intestine pick out all the best 

 part of the food that is in the water, and the waste 

 part which the mussel cannot use passes out of the 

 anus into the back-room, or cloacal chamber, and 

 is carried off by the current of water that is rushing 

 out by the dorsal siphon. Now, we have followed the 

 water which contains the air and food, into the mussel 

 and out again ; one part of it goes through the large 

 front-door, or ventral siphon, into the large front- 

 room, or ventral chamaer, over the gills through the 

 middle door, which leads into the little back-room, or 

 cloacal chamber, while the rest of the water goes 

 through the mouth, intestine, and anus, into the same 

 little room, or cloacal chamber, and then both parts go 

 out again through the little back-door, or dorsal si- 

 phon. Its journey is a long and useful one, for it gives 

 life to the mussel as it goes. If you wish to see it for 



