yi APPENDAGES 353 



lobes, while the exopodite is modified into a boomerang- 

 shaped plate, which, as we shall see, is an important 

 accessory organ of respiration. The first maxilla (4) is a very 

 small organ, having neither exopodite nor epipodite. The 

 mandible (3) is a large strongly calcified body, toothed along 

 its inner edge, and bearing on its anterior border a little 

 three-jointed, feeler-like body, the palp, the two distal seg- 

 ments of which represent the endopodite, its proximal 

 segment, together with the mandible proper, the protopodite. 



The antenna (2) is of great size, being nearly as long as 

 the whole body. It consists of an axis of five podomeres, 

 the fifth or last of which bears a long, flexible, many-jointed 

 structure, or flagellum (/), while from the second segment 

 springs a scale- like body or squame {ex). It is fairly obvious 

 that the two proximal segments represent the protopodite, 

 the remaining three, with the flagellum, the endopodite, and 

 the squame the exopodite. 



The antennule (i) has an axis of three podomeres ending 

 in two many-jointed flagella {fl. i, fl. 2), which are some- 

 times considered as corresponding to the endopodite and 

 exopodite. But in all the other limbs, as we have seen, 

 the exopodite springs from the second segment of the axis, 

 and the probabilities are that there is no exact corre- 

 spondence between the parts of the antennule and those of 

 the remaining appendages. 



The eye-stalks, already noticed, arise just above the an- 

 tennules, and are formed each of a small proximal and a 

 large distal segment. They are sometimes counted as 

 appendages serially homologous with the antennae and legs, 

 but are more properly to be looked upon as articulated pro- 

 cesses of the prostomium. It is probable that the anten- 

 nules are also -prostomial and not metameric structures : 

 assuming this to be the case, it will be seen that the 



Pbact. Zooi,. a a 



