VI UTTEODUCTIOlf. 



are the pleura, while the portion of the sternum interposed on 

 either side between the point of insertion of the appendage and 

 the pleuron is called the epimeron. Each of these segments is 

 found to possess a pair of appendages — the swimmerets—enah. 

 attached by a movable joint to the sternum. When one of these 

 appendages is detached, it is found to consist of a thick two- 

 jointed basal portion— the protopodite— and two long narrow 

 compressed laminae made up of numerous very short transverse 

 segments ; the outer and larger of these laminae is called the 

 exopodite ; the inner the endopodite of the appendage. In all 

 there are seen to be six segments having the general character 

 described above. The first three are rounded above ; but the 

 rest, especially the last, present a sharp dorsal keel, and the 

 appendages of the first and of the last segments differ considerably 

 in shape and position from those of the others. The appendages 

 of the first segment are uniramous in both segments ; in the 

 male a broad membrane — the petasma — is attached by, a narrow 

 stalk to the basal joint, and is united to its fellow in the middle 

 line by a series of minute hooked spines ; in the female the 

 petasma is rudimentary ; in the male, but not in the female, the 

 second pair of appendages has a rudimentary third branch. The 

 last pair of appendages are articulated at the hinder extremity of 

 the segment, instead of being attached near the middle of the 

 under surface ; the basal portion — protopodite- — is very large and 

 stout, and the endopodite and exopodite are developed into 

 broad plates. Lying between and above these appendages, and 

 articulating with their segments, after the manner of an additional 

 segment, is a narrow pointed body — the telson. The whole of 

 this hinder jointed portion of the body of the Prawn is called 

 the abdomen. The anterior, apparently unjointed, portion of 

 the body is called the cephalothorax. The apparent absence of 

 segmentation is due to the development of the great dorsal shield 

 or carapace, into which the dorsal portions of the skeleton of the 

 segments have coalesced — the several segments being, with- the 

 exception of the last, so intimately connected and fused as to be 

 incapable of motion on one another. On the lower or ventral 

 surface of the cephalothorax, however, the segmentation is 

 distinct enough — the sterna of the constituent somites being 

 readily traceable. The carapace is produced in front into a long 



