88 



THE CRUSTACEA 



The later nauplius stages pass without any sudden change into 

 the metaiwuplius (Fig. 49, B, C), in which the dorsal shield becomes 

 marked off and several pairs of appendages appear as rudiments 

 behind the mandibles. According to the earlier investigations of 

 Glaus, 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 arising from the fact that 



FIG. 40. 



Larval stages of Calan-usfinmanhicus^Crtochilus septentrionalix). A, nauplius; B, early 

 metanauplius ; C, later metanauplins. 1, antennule ; 2, antenna ; 3, mandible ; 4, maxillula ; 

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

 second pairs of swimming-legs ; an, anus ; g, brain ; gz, genital cells ; m, mouth ; me, primitive 

 mesoderm cells ; ol, labrum. (After Grobben, from Korschelt 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, which 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 characters 

 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 



