of the Fishery Board for Scotland. 159 
with a fringe of plumose sete. These resemble the sete with which 
the exopodites of the maxillipedes of the Zoéa are supplied. 
The first—fourth pleopods are formed of a single protopodite 
joint (Fig. 130), from which rise the paddle-like exopodite, ew, and the 
short oval endopodite, en 7. 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 setz, which, shortest proximally, increase in length 
the more distal their origin (Figs. 142, 132,130, and 141). There are 
usually 11 sete on the exopodite of the first and fourth pair of 
pleopods, and 12 (or 13) on the second and third pleopods. In each 
ease there are two terminal setz, 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 sete 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 setz on the exopodite. In the case of two second pairs of 
pleopods, in each the exopodite on one side had 13 sete, 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 stiffening the pair into a single double-paddle, and thereby 
increasing its efficiency. 
The endopodite is not completely segmented off from the proto- 
podite (Fig. 154). It isa 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 sete, two terminal, two on the outer edge, and one 
on theinner edge close to the apex of the joint. The respective leng hs 
of the setz 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 AspomEn (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 
non-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 (¢, Fig. 164) on the eleventh somite (i.e. 
that to which the second pereiopods belong). Inthe 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 
‘‘needle- point ” cilia. 
