II.] 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. 



8. 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 first 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, 



