30 



OUTLINES OP NATURAL HISTORY. 



Fig. 13.— I. Lobster with all the appendages except the last pair of swim- 

 inerets removed, and the segments of the abdomen slightly sejiarated 

 from one another, ca The great shield covering the head ; t The last seg- 

 ment of the abdomen left in connection with the last segment but one. 

 2. One of the segments of tlie abdomen, showing the typical structure of 

 a segment and of the appendages; t Upper arch of the segment; s Lower 

 arch ; p Plate prolonged downwards from the line where the upper and 

 lower arches unite ; a Base of the appendage ; 6 and c Outer and inner 

 branches of the appendage. 3. One of the last pair of foot-jaws, carrying 

 a gill ((/). 



