148 GENERAL ZOOLOGY 



About the mouth are six pairs of appendages. The first, 

 the hard mandibles (Fig. 83), are adapted to crushing into 

 smaller bits the food seized by the large claws. Each mandi- 

 ble bears a short palpus (Fig. 84, III, 2). Next in the series 

 are the first and second maxillse (Fig. 84, IV, V) and the first, 

 second, and third maxillipeds (Fig. 84, VI, VII, VIII). The 

 maxillipeds help to hold the food in place at the mouth ; the 

 maxillae also assist in this, and probably, with the wall of 

 the mouth cavity, are the seat of the sense of taste. The 

 second pair of maxillae also act as " gill-bailers' ' (Fig. 84, 

 V, 3-4; Fig. 85), which, by their motion, help to maintain 

 a current of water in the gill chamber, thus providing oxygen 

 for respiration. The separation between head and thorax is 

 understood to come between the second maxillae and the 

 first maxillipeds, thus making five pairs of appendages in 

 the head region. 



After the maxillipeds the next thoracic appendages are 

 the large claws, or chelipeds (Fig. 83), composed of seven 

 segments, of which the last two from the body, or distal two, 

 are modified to form a nipper, with which the animal cap- 

 tures and holds even rapidly swimming fishes. The remain- 

 ing thoracic appendages are the four pairs of walking legs 

 (Fig. 83; Fig. 84, XI, XII), also composed of seven seg- 

 ments, the first two pairs with nippers at their ends, and 

 the last two pairs without nippers. The three pairs of 

 maxillipeds, the one pair of chelipeds, and the four pairs 

 of walking legs constitute the eight pairs of appendages of 

 the thorax. 



The Abdomen. There are six pairs of appendages on the 

 abdomen. The first abdominal appendages of the female are 

 small, single, and thread-like; in the male (Fig. 83) they 

 are long and rigid, differing considerably from all the others 

 except the second pair. The second abdominal appendage 

 in the female is like the third. The third, fourth, and fifth 



