COMPARISON OF SOW-BUG AND CRAYFISH. 163 



beneath the head. Pick this apart with the needle. How 

 many pairs * of mouth- parts can you find ? Counting all 

 the appendages of the head, how many segments should 

 there be in this region ? 



COMPARISONS. 



With one column for crayfish, the other for sow-bug, 

 give answers to these questions : 



(1) Are head and thorax united ? 



(2) Are the eyes on movable stalks ? 



(3) How many pairs of walking-feet, counting the 

 pincers as such ? 



(4) Where are the gills ? 



(5) Are both exopodites and endopodites present ? 



* The two of the hinder pair are united, but should be counted as 

 a pair. 



