INVEBTEBRAXA. 



305 



The mandible consists of a very stout, hard, unjoiuted proto- 

 podite, serving as a biting organ ; and a small three-jointed endo- 

 podite, serving as a feeler or palp. The reason for calling this 

 endopodite and not exopodite will be found by comparing it with 

 the next two or three appendages behind. 



The first maxilla is a small, thin appendage, consisting of three 

 curved chitinous plates : these are shown, by comparison with the 

 next two, to be the two joints of the protopodite and the un- 

 jointed endopodite, respectively. 



The second maxilla consists of a portion resembling the first 



J. 



Fig. 150. APPENDAGES OF ASTACUS. 



(After Huxley.) 1, Mandible ; 2, first maxilla ; 3, second maxilla ; 4 5 and 6, first, 

 second, and third maxillipedes. All are drawn in the inverted position (dorsal 

 part downwards.) 



maxilla, but larger, and a more lateral portion called the teo^Jio- 

 gnathite. The two joints of the protopodite are each cleft nearly 

 into two ; the endopodite is unjointed but rather long. The 

 scaphognathite is a large flat, flexible plate: it has a special 

 function in connexion with respiration ( 20), and is regarded as 

 representing exopodite and epipodite united. 



7. Thoracic Appendages. The first maxillipede shews the same 

 flattened, expanded condition of the two protopodite-joints as the 

 appendages in front; the endopodite is small; the exopodite is 

 large and consists of a stout, unjointed proximal half and a flexible, 

 jointed distal portion ; while the epipodite is a thin ovate plate 



ZOOL. 20 



