PALINURUS OR THE SPINY LOBSTER OF BOMBAY. 369 



The whole of this lateral structure, including the basal calcified 

 podomere articulating with the coxopodite. the gill and the leaf or 

 lamella is called the epipodite. The surface of the lamella and 

 especially its margins bear a number of hairs. It is formed of a double 

 layer of chitinous cuticle. Its function is unknown but it may 

 prevent the filaments of contiguous gills becoming entangled. 



The basipodite is movably articulated with the coxopodite, but 

 distally it is firmly united with the proximal joint of the endopodite 

 so that it may easily be mistaken for a portion of the latter limb- 

 segment which is known as the ischiopodite (Greek ischion, the hip). 

 A well marked notch at the inner margin indicates the point at 

 which the two segments are fused. 



That this is the true homology or explanation of the structure will 

 be at once admitted on comparing the corresponding limb of a Cray- 

 fish or Lobster in which there is a distinct movable articulation 

 between the basipodite and ischiopodite, of which we have only a 

 notch left as a vestige in Palinurus. 



This ankylosis or immovable union of the basipodite and ischipodite 

 is characteristic of all the thoracic limbs of Palinurus whereas in the 

 Lobster we find the joint ankylosed in the great pair of chelae or 

 pincers, and in the third maxilliped only ; the second maxilliped and 

 all the walking legs have a freely movable joint between the basipodite 

 and ischiopodite. To the latter is movably articulated the merpodite 

 (Greek me ran, a thigh), the longest segment of this limb. Next 

 comes a short triangular piece, the carpopodiie (Gr. karpos, wrist), 

 next a propodite (pro, in front), a broad flat segment with a concave 

 distal margin to the centre of which is articulated the terminal 

 dacty'opodiie (Gr. dactylon, a finger). All these podomeres of the 

 endcpodite are more or less flattened to form horizontal plates, the 

 inner margins of all being covered with stiff bristles or setce. 



The exopodite is a long many-jointed palp-like flattened filament, of 

 which the proximal piece is as long as all the others — about seven — 

 taken together. 



We may regard a typical appendage as made up of a proximai stem 

 or protopodite of two segments, coxopodite and basipodite. The 

 coxopodite bears laterally an epipodite with its gill and lamina. To 

 the distal end of the basipodite an endopodite and exopodite are 



