CR USTA CEA—MALA COSTRACA . 387 



visible from above in the Brachiura, where it is bent under. It 

 consists of seven joints, of which the terminal one is the tail-piece 

 or telson. The first six abdominal segments are commonly supplied 

 with appendages. 



Appendages. — The cephalothoracic appendages fall into two 

 groups, the pre-oral, and the post-oral. The former comprise 

 three pair, the stalked eyes, and the two pair of antennce, which 

 vary greatly in length. The antennae consist of a three-jointed 

 shaft (scaptis) and a flagellum {funiculus) which in the first or 

 inner (anterior) pair (antennules) , is double or even triple, while 

 in the second or outer (posterior) pair it is single. Attached to 

 the first joint of the shaft of the outer antenna, or to a distinct 

 outer division of it, is the antennal scale, which is variously formed, 

 and has independent motion. 



The post-oral appendages of the cephalothorax, comprise six 

 masticatory and five locomotor pairs. In its typical development, 

 the crustacean limb is biramous, consisting of an inner branch 

 (endo p dite) , 2ind an outer branch (exopodite) , both, many jointed, 

 and arising from a common shaft or stem (protopodite) com- 

 posed of two segments. Many modifications occur, and one or 

 the other branch may be entirely wanting. 



The first pair of post-oral appendages form the hard chewing 

 jaws, or mandibles, each with a masticatory edge. These edges 

 meet between the upper lip (labrum), and the lower lip (labium, 

 paragnathce) . The next two pairs are the maxillce (anterior and 

 posterior), and the three remaining ones the maxillipeds (inner or 

 first, middle or second, and outer or third). The second and third 

 maxillipeds carry gills and in that respect resemble the locomotor 

 appendages. The first pair of maxillae is small, compared with 

 the mandibles, and of a delicate membranaceous character, hence 

 not likely to be preserved. The second pair generally shows the 

 biramous character more clearly than the first. The first maxilli- 

 ped is still furnished with a masticatory edge, as in the preceding 

 parts, but the second and third maxillipeds are without this edge. 

 The three maxillipeds agree in having the exopodite feeler-like, 

 while the endopodite is well developed and leg-like in the second 

 and third maxilliped. 



The locomotor appendages or legs proper (pcrciopoda) are in 



