CRUSTACEA. 



467 



biramous, and an unsegmented body. The second pair of antennae has not 

 however the colossal dimensions so common in the lower types. A mouth is 

 present, but the anus is undeveloped. 



After the first moult three pairs of prominences the rudiments of the 

 two maxillas and ist maxillipeds arise behind the Nauplius appendages 

 (fig. 212). At the same time an anus appears between the two limbs of 

 a rudimentary caudal fork ; and an unpaired eye and upper lip appear in 

 front. After another moult (fig. 212) a lower lip is formed (UL} as a 

 pair of prominences very similar to true appendages ; and a delicate 

 cephalo-thoracic shield also becomes developed. Still later the cutting blade 

 of the mandible is formed, and the palp (Nauplius appendage) is greatly 



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



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 

 maxillre ; mf. maxilliped i . 



reduced. The cephalo-thoracic shield grows over the front part of the 

 embryo, and becomes characteristically toothed at its edge. There are also 



302 



