THE LIFE OF THE UNIO 55 



animal is feeding. The Branchial and Anal openings are 

 expanded and the palpi flap rapidly, which draws the 

 current of water through the branchial opening. The 

 water goes through the gills and aerates the blook, then 

 it passes into the mouth and through the intestinal canal, 

 carrying in various microscopical organisms which are 

 filtere from the water and constitute the food of the 

 mussel, and the water passes out through theanal opening. 

 The mussel also separates sufficient lime from the water 

 to form its shell. 



There is quite a difference in the length of lives of 

 various mussels. Some of the Quadula group probably 

 require ten or twelve years to reach maturity and then 

 continue to live for many years. 



Some niggerheads have the appearance of being twen- 

 ty-five years old. Some of the Lampsilis group attain 

 a fair size in four or five years. In young shells of 

 some varities such as the Lampsilis ventricosus, or pocket- 

 book, and Lampsilis anadontoides, or yellow sand shell, 

 the winter rest periods are very plainly marked. In 

 most mussels, however, it is very difficult to determine 

 the age. 



The various kinds of mussels have different time, 

 for spawning. Every month in the year is the spawning 

 season of some variety. After ovulation the eggs pass 

 into portions of the mussel's gills which are termed mar- 

 supium. These serve as brood pouches for the retention 

 and maturity of embryos and glochidia until they leave 

 the mussel. When the embryos have remained in the 

 marsupium of the mussel for a period of time which 



