of the Fishery Board for Scotland.. 



159 



with a fringe of plumose setie. These resemble the setse with which 

 the exopodites of the maxillipedes of the Zoea are supplied. 



The first — fourth pleopods are formed of a single protopodite 

 joint (Fig. 130), from which rise the paddle-like exopodite, eaj, and the 

 short oval endopodite, en ih. The pleopods differ in size. Of the first 

 four, the first is the largest, the fourth is the smallest, and the second 

 and third are intermediate in size. 



From the margin of the distal half or two-thirds of the exopodite 

 project the plumose setse, which, shortest proximally, increase in length 

 the more distal their origin (Figs. 142, 132, 130, and 141). There are 

 usually 11 setae on the exopodite of the first and fourth pair of 

 pleopods, and 12 (or 13) on the second and third pleopods. In each 

 case there are two terminal setse, and four on the external margin. 

 In the first and fourth pleopods there are five on the internal margin, 

 and in the second and third pleopods six set?e on that edge. But the 

 number on the internal edge varies. I have not noticed any variation 

 in the number of the outer series, though it probably exists. No 

 number greater than seven was found on the inner margin, making 

 13 setae on the exopodite. In the case of two second pairs of 

 pleopods, in each the exopodite on one side had 13 setas, and on the 

 other side the exopodites had 12 and 11 respectively. 



The endopodite bears on the internal face of its extremity three or 

 four curved hooks (Figs. 134 and 136). By means of these the 

 endopodites of a pair of pleopods are locked to one another, in this 

 way stifiening the pair into a single double-paddle, and thereby 

 increasing its efliciency. 



The endopodite is not completely segmented ofi* from the proto- 

 podite (Fig. 134). It is a rigid process of the latter. At its junction 

 with the basal joint there is a large bulbous thickening of the integu- 

 ment, which serves to strengthen and give elasticity and rigidity to 

 the part. The hooks, too, arise from a thickened bed of chitin. 



The fifth pleopod is a single-branched appendage ; it consists of two 

 joints (Fig. 127, a). The first joint has a broad base. The second joint 

 bears five plumose seta", two terminal, two on the outer edge, and one 

 on the inner edge close to the apex of the joint. The respective lenghs 

 of the seta3 are shown in the drawing. This pleopod lies beneath the 

 telson, and in a dorsal view of the abdomen is hid by it. 



1. The Abdomen (Figs. 145 and 151) now in general form resembles 

 the adult condition. In the adult the shape of the abdomen is a sexual 

 character, that of the female being broad, that of the male narrow. 

 In this, the first young stage, we have an intermediate condition, a 

 nou-sexual state. It is narrower in comparison than the abdomen of 

 the female and broader than that of the male. 



The abdomen no longer functions as a swimming organ ; it is tucked 

 up against the thorax, to which it adheres closely, lateral movement 

 being prevented by the tubercles (t. Fig. 164) on the eleventh somite {i.e. 

 that to which the second pereiopods belong). In the adult the tubercles 

 fit into depressions on the sixth abdominal segment. They prevent 

 lateral movement of the abdomen, and their function in this stage is 

 probably a similar one. They are much larger in the adult male than 

 in the female crab. 



The abdomen is profusely adorned over its dorsal surface with ciliated 

 hairs (Fig. 128). The arrangement and number of these is shown in 

 Fig. 151. Over the telson and the lateral parts of the dorsum of each 

 segment except the first, there are considerable numbers of the minute 



aeeile point " cilia, 



