Dr. F. Miiller on Balanus armatus. 403 
frequently, at the same place, several groups of very delicate 
ints. 
P The middle joints of the outer branch also bear, within the 
toothed armature, from two to four pairs of sete; with these 
are sooner or later associated at first a single, and afterwards 
several rows of sete. on the inner margin of the upper end of 
the joints, and finally, on the last joints, a dense irregular coat 
of sete which often covers a great part of the inner surface. 
On the inner branch the sete of the inner surface are more 
numerous, even on the lower joints. 
Fourth to sixth pairs: the cirri of the last three pairs of 
feet are rarely all found uninjured ; sometimes one, sometimes 
another of them wants a larger or smaller piece. ‘These losses, 
as is well known, are more or less completely replaced by the 
formation, in the last of the remaining joints, of a number of 
new joints, which come into use after the next change of skin. 
The frequency of such mutilations scarcely allows us to say 
anything as to the number of joints in these cirri. In the last 
pairs this may exceed forty-five, and their length is often more 
than three times that of the third pair. The joints of all these 
cirri are thinner, but much longer, than those of the anterior 
pairs; the upper joints almost always bear on the flexed side 
og] pairs of sete, but frequently only three in the fourth pair 
ot feet. 
In the fourth pair the dorsal surface of the first joint of the 
outer branch is usually armed with rather strong denticles 
directed upwards; on the middle joints of both branches, but 
especially the outer one, besides the short pointed spines, and 
in their vicinity, more or less numerous spines directed up- 
‘wards are scattered over the outer surface of the joint; in rare 
instances these spines become converted, on the outer branch, 
into slightly curved teeth directed downwards, so as to produce 
an armature similar to that of the third pair, although certainly 
weaker (fig. 22). | 
The fifth pair of feet is distinguished by a strong, some- 
what curved tooth, directed upwards, which stands at the com- 
-mencement of the dorsal surface of the second peduncular 
jot; this is usually followed by a similar smaller tooth, or 
more rarely by two. ‘These are seldom altogether wanting. 
On the sixth pair of feet the peduncular joints and the first 
joints of the cirri have their dorsal surface covered with very 
numerous, short, close-sitting points, directed upwards. 
Penis.—At the base of the penis, between it and the anus, 
the usual conical process exists; the penis, which is extensible 
to several times the length of the cirri, is beset-only with a 
few short hairs. 
