250 



THE CRUSTACEA 



characterised chiefly by changes in the antennules and antennae. 

 The former, which have become biramous already in the Calyptopis- 

 stage, now elongate, while the latter lose their natatory function, and 

 their rami, at first similar, become differentiated into " scale " and 

 flagellum respectively. The Cyrtopia gradually assumes the form 



Larval stages of Euphausia. A, metanauplius. B, calyptopis. C, later calyptopis-stage. 

 1, antennule ; 2, antenna ; 3, mandible ; 4, maxillula ; 5, maxilla ; I, first thoracic appendage ; 

 th, thoracic somites ; rili, abdomen ; (cijXfts), first five abdominal somites ; , uropod ; an, anus ; 

 f.s, frontal sense-organs. (A after MetschnikofT; B and C after Claus ; from Korschelt and 

 Heider's Embryology.) 



of the adult by the successive development of the remaining 

 thoracic limbs. 



The development of the various appendages, which has been 

 traced in detail by Sars, offers many features of interest. The palp 

 of the mandible only begins to redevelop in the Cyrtopia- stage. 

 The maxillula has at first a small lobe on its outer edge which 

 appears to represent the exopod and is quite independent of the 



