The Crayfish. 



37 



(Fig. 1 8, B), is much the same, but the endopodite has com- 

 menced to deteriorate, and the exopodite is now larger. 

 In the first pair of maxilUpedes (Fig. i8, A) the protopodite 

 has changed into two perfectly separated flattened plates, 

 which are applied to the sides of the mouth, and are clearly 

 jaws ; the endopodite has become quite small, and the exo- 

 podite large in proportion. In front of these are the two 

 pairs of maxillae. The last pair of these is not very different 

 from the first maxillipedes ; but the two joints of the proto- 



FlG. i8.— A, first, B, second, maxillipede of Crayfish. (After Huxley.) 

 e, ep, epipodite ; en, endopodite ; ex, exopodite ; other letters as in Fig. i6- 



podite are still more flattened and jaw-like, and each joint has 

 become partially separated into two. The endopodite is still 

 small, and the exopodite is fused with a flat plate, present in 

 the appendages lying behind, and there associated with the 

 gills {q.v^, the so-called epipodite. In the first pair of maxillse 

 the protopodite is all of functional importance that remains of 

 the appendage, but there is still a small endopodite. Finally, 

 there are the mandibles, in which the protopodite forms a 

 massive chewing organ, to which is appended a small and 

 jointed endopodite. We can trace, therefore, in the series 

 of mouth appendages, a gradual change from ambulatory 



