SEA-FISHERIES LABORATORY 



319 



which this segment is capable is almost in a vertical 

 plane. The two hinges of the carpos (C. 1 ) are situated 

 dorsally (d 3 ) and ventrally (v 3 ), and the segment moves 

 forward and downward. The propodite (P.) has two 

 hinges — dorsal (7Z 4 ) and ventral (y^). The former is 

 external to the latter, and the segment moves forward 

 and slightly upward. In the dactylos (D.) the hinges are 

 horizontal and the segment swings in a vertical plane. 



The dimensions of the various segments of the chela 

 in a female crab (carapace breadth 23*5 cm.) are as 

 follows : — 





Anterior length. 



Posterior length 



Coxopodite . . . 



7 mm. 



11 mm. 



Basi-ischiopodite 



17 „ 



6 „ 



Meropodite ... 



19 „ 



... 32 „ 



Carpopodite . . . 



... 10 „ 



... 30 „ 



Propodite 



... 50 „ 



... 20 „ 



Dactylopodite 



... 20 „ 



... 30 „ 



The dorsal sides of the basi-ischium and of the meros 

 are flattened so that they can be closely applied to the 

 anterior portion of the sub-branchial and sub- hepatic 

 regions of the carapace, and in these places setae are 

 absent from the carapace. 



Between the meros and the carpos the limb is capable 

 of bending on itself, so that the anterior borders of the 

 propodite and the carpos become closely applied to the 

 anterior borders of the basi-ischium and the meros. 



On the dorsal side of the basi-ischium and meros 

 there are irregular grooves. These are the lines of 

 absorption (PL II, fig. 12, abs.) (see section on Ecdysis). 



Pereiopods 2-5 (PL II, fig. 13). These are known as 

 the " walking legs." Their essential structure is the 

 same as that of the chela. The one obvious difference is 

 that in all the walking legs the propodite has not an 



