60 CRUSTACEA. 



wrists side l)y side, placing die fingers down on a 

 level table; bind the wrists by an elastic band, hold 

 diem well up from the table, so as to show the fingers. 

 Then let one set crawl while the other pushes, so as to 

 keep up a continuous motion sidewise without assist- 

 ance from the arms. The terminal sections of the 

 legs show wear only on the points where these are in- 

 serted in the ground. 



Some of the Brachyura not only walk, but also swim 

 rapidly sidewise with oar-like paddles which are de- 

 veloped from the fifth pair of walking-legs. The blue 

 crab of southern New England, ( 'allinectes hastatus, is 

 a common type of this group. 



The Fiddler crab (Fig. 28) is smaller than the com- 

 mon crab, though like it in important structural charac- 

 ters. One of the arms of the male is very much larger 

 than the other, giving a peculiar appearance to the ani- 

 mal, which is supposed to remind one of a violin. The 

 large arm is used in fighting, which accounts for its 

 size and strength. The females have little inclination 

 to battle, and both arms are small. Thus, though the 

 two arms are naturally, or, as we might more strictly 

 say, normally equal, one becomes larger by the more 

 active use it is put to by the male, for the same reason 

 that our right arm becomes larger than our left. Occa- 

 sionally crabs are found which are left-armed, just as 

 our children are sometimes left-handed.* 



* If teachers could but sec the true meaning of such facts, 

 and apply them, they would abandon the practice of confirming 

 children in the habit of making themselves one-sided, and would 

 encourage them to use both hands. One of these days this cus- 

 tom of teaching children to use the right arm and right side, to 



