THE LOBSTER AND OTHER CRUSTACEANS. 83 



pairs have but two, and the inner one of these (Fig. 87, end) is very 

 large and resembles one of the legs ; the other divisions are two- or 

 many-jointed and act as feelers. 



Now, if we count all the appendages we shall see that there are in 

 all nineteen pairs, as follows : 



Head. 



1st Segment. First pair of antennae. 



3d " Second pair of antenna?. 



3d " Jaws (mandibles). 



"4th " First pair of accessory jaws (maxillae). 



5th " Second pair of accessory jaws (maxilla?). 



6th " First pair of foot- jaws (maxillipedcs). 



7th " Second pair of foot- jaws (maxillipedes). 



8th " Third pair of foot-jaws (maxillipedes). 



Mid-body or Chest. (Thorax.) 

 9th " First pair of chest-legs. 

 10th " Second pair of chest- legs. 

 llth " Third pair of chest-legs. 



12th " Fourth pair of chest legs. 



13th " Fifth pair of chest-legs. 



Hind Body. (Abdomen.) 



14th " First pair of abdominal k-gs. 



15th " Second pair of abdominal legs. 



16th " Third pair of abdominal legs. 



17th " Fourth pair of abdominal legs. 



18th " Fifth pair of abdominal legs. 



19th " Sixth pair of abdominal legs. 



, as a rule, and this applies to several thousand species of the 

 class of Crustaceans, there is but one pair of limbs to a segment. 

 Hence in the head, where it is impossible to count the segments, as 

 they are incomplete, there are eight segments, one to each pair of ap- 

 pendages ; and in the mid-body (or thorax), which is covered by the 

 shield, which really is a part of the head, there are five segments, one 

 for each pair of feet ; and, finally, there arc in the hind body (or ab- 

 domen) six segments which bear legs, besides a seventh rudimentary 

 one, so that we have twenty segments in a lobster's body. These seg- 

 ments are collected into threi regions, thus : 



Head ............................ 8 segments. 



Mid-body ......................... 5 



Hind body ........................ 7 



20 body segments, 



