14 THE LIFE OF CRUSTACEA 



while the two segments of the protopodite become 

 flattened and broadened inwards to form the jaw- 

 plates. The mandibles (Fig. 5, D), which are the 

 chief organs of mastication, consist mainly of the 

 much enlarged basal segment of the protopodite, 

 with a strongly toothed inner edge, where it works 

 against its fellow of the opposite side ; and the rest 

 of the limb is reduced to a small sensory " palp," 

 which represents the second segment of the protopo- 

 dite and the endopodite. 



The antennae (Fig 5, C) can be shown, without 

 difficulty, to conform to the same plan of structure 

 as the other appendages. The two segments of the 

 protopodite are short, but distinct ; the endopodite 

 forms the long lash, or flagellum, composed of very 

 numerous small segments ; the exopodite is reduced 

 to a small movable scale or spine. 



The antennules (Fig 5, B) seem at first sight to 

 present the two-branched type of structure in its 

 simplest form ; but there is considerable doubt as to 

 whether the two lashes which each bears on a three- 

 segmented stalk are really equivalent to the endopo- 

 dite and exopodite. 



The movable stalks which carry the eyes (Fig. 5, A) 

 have been considered by some to belong to the series 

 of the appendages, and to be, in fact, modified limbs. 

 If this be the case, we have here the greatest simpli- 

 fication which the limb undergoes in the Lobster, for 

 each eye-stalk consists only of two segments : the 



