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FIRST BOOK OF ZOOLOGY. 



right side of the animal. The forward end will be the end 

 away from him, and the hinder end will, of course, be the 

 end toward him. (See Fig. 35.) 



29. Let the pupils now endeavor to collect some fresh- 

 water mussels alive. These may be found partly buried in 

 the sand or mud of rivers and lakes. As they crawl along 

 partly buried in this way, they plough up the sand, leaving a 

 well-marked furrow or groove behind them. Every boy 

 that goes in bathing is familiar with the peculiar furrow left 

 by the fresh-water mussel. By following such a furrow, the 

 mussel that made it will soon be found. 



Fig. 36 represents the appearance of a common fresh- 

 water mussel in the act of crawling. 



Fig. 36.— Showing Position of Mussel when crawling.-/, foot buried below the surface 

 of the sand s. Above the line s is supposed to be water, the line representing the bottom 

 of a lake or river. 



Having collected a few in this way, they may be placed 

 in a large, shallow pan of water, and allowed to remain quiet 

 for a while. Gradually the shells will open a little, and from 

 the hinder end a curious fringed border appears ; on examin- 



