CRUSTACEA. 



387 



differentiations. They remain however very simple ; the maxillipeds 

 especially are very short and resemble somewhat Phyllopod appendages. 



Up to this stage the tail has remained rudimentary and short, but 

 after a further ecdysis (Glaus) it grows greatly in length. At the same 

 time the cephalo-thoracic shield acquires a short spine directed backwards. 

 The larva is now in a condition to which Claus has given the name of 

 Protozoaea (fig. 213 A). 



Very shortly afterwards the region immediately following the segments 

 already formed becomes indistinctly segmented, while the tail is still with- 

 out a trace of segmentation. The region of the thorax proper soon be- 

 comes distinctly divided into seven very short segments, while at the same 

 time the now elongated caudal region has become divided into its normal 

 number of segments (fig. 213 B). By this stage the larva has become 

 a true Zoaea though differing from the normal Zoaea in the fact that 

 the thoracic region is segmented, and in the absence of a second pair of 

 maxillipeds. 



FIG. 212. NAUPLIUS OF EUPHAUSIA. (From Claus ; after Metschnikoff.) 

 The Nauplius is represented shortly before an ecdysis, and in addition to the proper 



appendages rudiments of the three following pairs are present. 



OL. upper lip; UL. lower lip; Md. mandible; MX', and MX", two pairs of 



maxillae; mf. maxilliped 1. 



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