II.] THE CRAYFISH AND LOBSTER. 197 



The above description applies equally to both 

 Lobster and Crayfish, except that in the former 

 animal the epipodite and gill are in no way con- 

 fluent. 



c. The third inaxilUpede. Its protopodite ; much as in 

 ^, except that its distal segment is ankylosed with 

 the basal one (ischiopodite) of the endopodite. 

 Its endopodite; greatly increased in size and im- 

 portance, as compared with that of b. The five 

 segments enumerated for b can be recognized ; the 

 ischiopodite is the longer of the series, the others 

 become relatively shorter in proportion as the free 

 end of the appendage is approached. The inner 

 edge of the ischiopodite is beset by a single series 

 of crushing teeth. Its exopodite; structurally identi- 

 cal with that of b^ but considerably shortened up. 



Note the presence of a tuft of long setae {coxo- 

 poditic setce) arising from the base of the epipodite. 



In the Lobster, the ischiopodite bears two rows of 

 teeth and the meropodite one row. 



d. The great chela ; much larger and more powerful 

 than the last appendage, but resembling it in 

 general structure, and in the ankylosis of its ischio- 

 podite and basipodite ; it also carries a gill. 



The exopodite is entirely suppressed. The 

 ischiopodite is relatively short, the meropodite and 

 propodite being, as in b, the longer of the series of 

 segments. The propodite; greatly enlarged and 

 prolonged outwardly to form, with the dactylopo- 

 dite, an opposable forceps (chela). 



e. The four posterior thoracic appendages {ambulatory 

 appendages). 



