NO. 10 



CRUSTACEAN METAMORPHOSES — SNODGRASS 



53 



median eye, and a large labrum. The metanauplius (B) acquires three 

 additional pairs of appendages, which are the first and second maxillae 

 and the first pair of legs (iL), or maxillipeds. The mandibles (Md) 



Fig. 20. — Euphausiacea. Life-history stages. (A-E from Heegaard, 1948; F, G 



from Lebour, 1925.) 



A, Meganyctiphanes norvegica Sars, nauplius. B, same, metanauplius. C, 

 same, first calyptopis instar. D, same, third calyptopis instar. E, same, first 

 furcillia instar. F, Nyctiphanes couchii Bell, last (12th) furcillia instar. G, 

 Meganyctiphanes norvegica, first cyrtopia instar. 



have become jawlike. The metanauplius is followed by the calyptopis 

 stage, which at an early instar (C) is characterized by the distinct 

 development of the carapace and the elongation of the abdomen. The 

 median eye is replaced by sessile rudiments of compound eyes con- 

 cealed beneath the carapace. The appendages are those of the meta- 

 nauplius. At a later calyptopis instar (D) the abdomen has become 



