322 



THE CRUSTACEA 



one terminating in a strong curved spine. A vestigial palp is 

 present (^). 



The maxillae (Fig. 189, C) have a peculiar and characteristic 

 form which cannot be closely compared vi^ith that of the corre- 

 sponding appendage in other Malacustraca. They appear to consist 

 of four segments, of which the first and second are indistinctly 

 separated. 



The first five pairs of thoracic appendages are similar in structure 

 and are commonly called maxillipeds, though, as they possess no 

 endites or other adaptations for mastication, the name is hardly 

 appropriate. Each consists of only six segments (there is no 

 evidence to show how these are related to the seven segments 

 commonly recognised in other Malacostraca) and terminates in a 



Fig. 189. 



Mouth-parts of Sq^dlla mantis. A, mandible, seen from the inner, or oral, side ; B, 

 maxillula ; C, maxilla, i, incisor process ; m, molar process ; o, papilla bearing opening (of 

 maxillary gland ?) ; p, palp. 



prehensile "hand" or sub-chela; there are no exopodites, but 

 epipodites (Fig. 190, A, ep) are present on all five pairs in the 

 form of discoid membranous plates or vesicles attached to the 

 basal segment by a narrow neck. The first pair of limbs (Fig. 190, 

 A) are long and slender and the terminal segment is minute ; the 

 second pair are very massive, forming powerful Aveapons (Fig. 186, 

 th^) ; the third, fourth, and fifth pairs resemble each other and are 

 less powerful. In each case the terminal segment is flexed upon 

 the preceding one in such a way that its point is directed forwards, 

 an arrangement which recalls the peculiar inverted chela of the 

 Amphipod TriscMzostoma. The last three pairs of thoracic limbs 

 (Fig. 186, tli^) are slender, biramous, and without epipodites. The 

 protopodite is very distinctly composed of three segments, of which 

 the second is elongated. The inner (and anterior) of the two 

 rami is the stouter and consists of two segments ; the outer is 

 slender and unjointed. According to Claus, the development of 



