THE CRAYFISH AND LOBSTER. 199 



terminal multi-articulate segment being shortened 

 up, in proportion as its basal one is elongated. 

 The latter is here at its maximum for the whole 

 abdominal series; it is produced up into an 

 accessory piece, which is segmented off and 

 modified to form a plate, rolled upon itself so 

 as to enclose a demicanal, concave inwardly. 



In the Lobster, this accessory process of the 

 basal segment of the endopodite is still more 

 marked. 



S. The first pair; in the female rudimentary, ex- 

 ceedingly variable in size and not unfrequently 

 absent altogether : except in very rare cases the 

 exopodite is suppressed. In the male the exo- 

 podite is invariably absent, the protopodite and 

 endopodite become ankylosed and terminate in 

 a plate rolled upon itself. In the Lobster the 

 terminal division differs slightly from that of the 

 Crayfish. 



g. The Jirs^ maxillipede. Its protopodite, flattened 

 and foliaceous, its two segments well defined; its 

 exopodite, substantially identical with that of a\ 

 its endopodite, reduced to a small two-jointed 

 structure, lying under cover of the basal joint of 

 the exopodite; its epipodite, fully developed but 

 destitute of a gill. 



In the Lobster, the reduction of the endopodite is 

 far less marked. 



h. The second maxilla. Its protopodite, foliaceous 

 like that of g^ but pectinated internally ; its endo- 

 podite, elongated and filamentous, its free end is 

 recurved to form a hook-shaped process which, 



