96 ESSENTIALS OF ZOOLOGY 



is borne a three-jointed palp ; the first of its segments is 

 believed to belong to the protopodite, and the other two to 

 form the endopodite. 



The first maxilla is rudimentary and consists of two leaf- 

 like protopodite elements and a two- jointed endopodite. Its 

 function in the adult is probably quite unimportant. 



The second maxilla, besides contributing to the mouth 

 apparatus, is greatly modified in connexion with respiration. 

 It consists of (a) a protopodite of two thin segments, each of 

 the lamellae being bi-lobed, (b) an endopodite, and (c) a long 

 flattened curved plate extending forwards and backwards 

 from the surface of attachment in the cervical canal. This 

 plate is called the scaphognathite, and is made up of the exo- 

 podite and an element allied to the gills called the epipodite. 

 In life it is constantly in movement, and in such a manner as 

 to bring about a forwardly moving current of water over the 

 gills. 



The first maxilliped is the smallest and consists of 

 (a) a small basal and a large distal segment internally, and 

 forming together the protopodite; (b) a two-segmented endo- 

 podite ; (c) an exopodite made up of a long narrow plate bearing 

 a short flagellum; and immediately above the latter is (d) a 

 thin flat epipodite. 



The second maxilliped is made up of a two- jointed proto- 

 podite supporting a well- developed endopodite of five segments, 

 a thinner rounded exopodite, and a small epipodite. The 

 latter is attached to the basal element of the protopodite and 

 lies in front of the gills. 



The third maxilliped, like the preceding, consists of a 

 two-jointed protopodite, bearing a large endopodite of five 

 segments, the basal one of which presents a row of teeth-like 

 spines on the inner edge anteriorly ; a small exopodite, rounded 

 and distally flagellate ; and a slender epipodite. 



The last five pairs of thoracic appendages, the pereiopoda 

 or walking legs, are characteristically well developed in the 

 1 Decapoda.' They agree with one another in consisting of a 

 two- jointed protopodite and a five-jointed endopodite. The 

 exopodite is suppressed, but it is present in the larva. The 

 first three are chelate and the last two simple. The basal 



