CRUSTACEA. 481 



with a long distinctly-segmented abdomen bent underneath the 

 thorax. The cephalo-thoracic shield covers over the front part 

 of the body, and is prolonged into a long frontal spine pointing 

 forwards, and springing from the region between the two eyes ; 

 a long dorsal spine pointing backwards ; and two lateral spines. 



To the under surface of the body are attached the anterior 

 appendages up to the second maxilliped, while the six following 

 pairs of thoracic appendages are either absent or represented 

 only in a very rudimentary form. The abdomen is without 

 appendages. 



The anterior antennae are single and unjointed, but provided 

 at their extremity with a few olfactory hairs (only two in 

 Carcinus Mcenas) and one or two bristles. The rudiment of the 

 secondary flageltum appears in very young Zoaeae on the inner 

 side of the antennules (fig. 223 At. /.). The posterior antennae 

 are without the flagellum, but are provided with a scale repre- 

 senting the exopodite (fig. 223 At. II. ex] and usually a spinous 



FIG. 224. CRAB ZO^EA AFTER TH.. THIRD PAIR OF MAXILLIPEDS AND THE 



THORACIC AND ABDOMINAL APPENDAGES HAVE BECOME DEVELOPED. 



at 1 , antenna of first pair ; at z . antenna of second pair ; mx l . first maxilla ; mop. 

 second maxilla ; mxp 1 . first maxilliped ; mxjP. second maxilliped ; mxf. third max- 

 illiped ; oc. eye ; ht. heart. 



process. The flagellum is very early developed and is repre- 

 sented in fig. 223, At. II. en. The mandibles (md) are large but 

 without a palp. The anterior maxillae (mx i) have a short two- 

 jointed endopodite (palp) with a few hairs, and a basal portion 

 B. II. 31 



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