METAMORPHOSIS OF CORTSTES CASSIVELAUNUS. 471 



This stage is characterised by the greater development of 

 the antenna^, gills> ^^^ pleopods, but otherwise shows no 

 essential difference from the preceding one. In the first 

 antenna the inner branch is more developed, and the outer 

 branch shows signs of segmentation beneath the cuticle and 

 an increased number of sensory rods. The base is much 

 swollen, and the auditory pit is forming. 



The second antenna has now a flagellum (endopodite) 

 nearly two thirds the length of the rostrum, showing two 

 distinct joints at its base and a number of indistinct joints 

 beneath the cuticle. The exopodite and spinous process are 

 relatively unimportant structures, and at the approach of the 

 moult their contents are absorbed and only the chitinous 

 cuticle remains. 



The first maxilla shows no change, but in the second 

 maxilla the setae are more numerous upon the scapliog- 

 nathite, though they are comparatively shorter than before. 



The epipodites of the first and second niaxillipedes are 

 larger, but neither podobranchs nor artlirobranchs are 

 formed. 



In the third maxillipede, however, the podobranch is being 

 separated from the epipodite, and the artlirobranchs are both 

 present. The anterior arthrobranch, however, shows no 

 signs of lamellar structure, though the posterior one, like the 

 succeeding pairs of gills, is distinctly lamellate. 



The s-ill formula at this stag-e is therefore as follows : 



