lOG 
THE VOYAGE OF H.M.S. CHALLENGEE. 
The dorsal cirri commence on the second bristled foot, then on the fifth, ^ud on 
every alternate foot to the twenty-third. The latter has one, and so has the twenty- 
fourth ; the twenty -fifth is blank. They then occur on the twenty -sixth, twenty- 
seventh, twenty-ninth, thirtieth, thii’ty-second, thirty-thhxl, and every succeeding one 
to the forty -seventh. The tail is represented by a long and large cutus of a similar 
character in the middle line beloW the anus, a peculiarity — if it were constant, which it 
is not — of considerable importance in regard to classification. The dorsal cirri of 
several of the last feet are longer than those in front. 
The first ventral cirrus (on the first bristle -bearing foot) corresponds in structure 
and appearance to the dorsal cirri ; and the others behind are somewhat longer than 
their successors. The latter also lose the clavate papillae on their surface. Toward the 
tail, on the other hand, the papillae again appear, and on the penultimate segment the organ 
resembles the anterior dorsal cirri. The average ventral cutus is a short tapering process 
wdiich reaches the bases of the ventral bristles. The ventral papilla is well developed, 
occurring on an eminence at the base of each foot. It has the form of a shghtly tapered 
truncate cone. 
The scales are fifteen on each side, the four anterior pairs only meeting in the 
middle line, those which follow leaving a considerable portion of the dorsum bare. 
Two or three of tlie terminal pairs, however, again meet in the preparations. The first 
occurs on the second foot (first bristled), the second on the fourth, the third on the fifth, 
the fourth on the seventh, and so on alternately to the tw^enty-thud. The thirteenth 
scale is placed on the twenty-sixth, the fourteenth on the twenty-ninth, and the 
fifteenth on the thirty-second foot. To the naked eye the scales are smooth, but they 
are really covered all over with minute spines (Transit of Venus Exped., pi. xv. fig. 1). 
The spines have in most cases a somewhat truncate tip. In section the scale is 
comparatively thin. The external margin is slightly curved upward in many. The 
scales in young forms almost entirely cover the dorsum, except the bare part at the tall. 
The foot consists of two well-marked divisions, and each has dorsally an inner 
tubercle for a scale, or a cirrus projects from the posterior part of the bristle-papilla, as 
in the previous families. It is interesting thus to notice the uniformity in regard to the 
arrangement of the processes. The bristles form a prominent border of a light brown 
colour along the sides, the dorsal being somewhat darker than the ventral. They are 
rigid, and easily penetrate the hand if pressure be made against them. The dorsal 
bristles are comparatively few in number, and radiate stiffly outwmrd from a conical 
papilla {o‘p. cit., pi. xv. figs. 2, 3). They increase in length toward the posterior end 
of the body. The spine of this division is black. 
The ventral bristles are in two groups, an upper smaller, situated rather above and 
behind the spine, and a large dense series placed in transverse rows below the spine. 
The superior group consists of stout bristles ; the inferior as usual diminishes in 
