APPENDAGES OF CRAYFISH 



225 



protopodite (2 segments) and endopodite 

 (5 segments). The larger basal segment 

 of the protopodite carries attached to 

 its outer surface (i) a flattened plate, 

 the epipodite (Fig. 103, 4, ep}, prolonged 

 into numerous slender processes which 

 constitute a breathing organ or gill, and 

 (2) a tuft of fine chitinous threads (/). 

 The three front pairs of walking legs 

 differ from that which has been described 

 in the fact that they are chelate, and in 

 the case of the front pair (chelipeds) the 

 chela is much enlarged (Fig. 102, A, Lj). 



The series of appendages in front of 

 the chelipeds and extending to the level 

 of the mouth is constituted by six pairs 

 the third maxillipeds (Fig. 103, Mp.$), 

 the second maxillipeds (Mp.2), the first 

 maxillipeds (Mp.i), the second maxillae 

 (Mx.2), the maxillulae or first maxillae 

 (Afac.i), and the mandibles (M) charac- 

 terized by loss of the primitive locomotor 

 function of the limb and specialization 

 in connexion with the act of feeding, 

 specialization which reaches its height in 

 the appendages nearest to the mouth. 

 Thus the endopodite and exopodite are 

 reduced in varying degrees as will be 

 seen in Fig. 103. 



In the case of the first maxilliped 

 and the two pairs of maxillae, flattened 

 plate-like gnathobases have grown out 

 from the inner side of the protopodite, 

 and in the mandible the limb has come to 



FIG. 103. 



Appendages of Crayfish as seen from the ventral side. 

 A i, First antenna ; A 2, second antenna ; en, endo- 

 podite ; ep, epipodite ; ex, exopodite ; 4, fourth 

 walking leg ; M, mandible ; Mp.i, first maxilliped ; 

 Mp.2, second maxilliped ; Mp.3, third maxilliped ; 

 Afar. i, first maxilla ; Af*.2, second maxilla ; n, external 

 opening of nephridium ; p, protopodite ; t, chitinous 

 threads. 



en. 



IX. 



en. 



Mx.\ 



en. 



en. 



Mx.2 



ep, 



ex. 



en. 



ep. 



Mp.2 



Mp.3 



