THE CRUSTACEA 



The later nauplius stages pass without any sudden change into 

 the metanauplius (Fig. 49, B, C), in which the dorsal shield l^ecomes 

 marked off and several pairs of appendages appear as rudiments 

 behind the mandibles. According to the earlier investigations of 

 Claus, the second pair of these rudiments were believed to give 

 rise to the " outer and inner maxillipeds," but, as stated above, 

 it is now known that this is an error arisino- from the fact that 



I-'lG. V.K 



Larva! stages of Caldnin' finmnrrjiivnx { = i'(inrhiJus septcntrinnuUa). A, iKinjilius ; 13, early 

 metanauplius; C, later inetanauiiliiis. 1, anti'iniiile ; i, antenna; 3, mandible; 4, nuixillula : 

 6, 5, maxilla and maxilliped (formerly regarded as parts of one appendage); I, II, tirst and 

 second pairs of swimming-legs ; an, anus ; g, brain ; <]z, genital cells ; m, mouth ; ■»«■, primitive 

 mesoderm cells ; ol, labrum. (After Grobben, from Ivorsclielt and Heider's Embryology.) 



in the metanaupliar stages of most Copepods the appendages are 

 very much crowded together. 



The transition from the metanaupliar to the Copepodid stages 

 (sometimes known as the " Cyclops stages ") is marked by a straighten- 

 ing of the body, Avhich in earlier stages is ventrally curved, and by 

 the unsegmented posterior region becoming sharply marked off from 

 the broader anterior part. The limbs begin to show the chai'actei's 

 which they have in the adult, the antennules elongating and becom- 

 ing divided into more numerous segments, the antennae losing the 

 masticatory process, and the mouth -parts and swimming-feet 



