Dr. F. Miiller on Balanus armatus. 403 



frequently, at the same place, several groups of very delicate 

 points. 



The middle joints of the outer branch also bear, within the 

 toothed armature, from two to four pairs of setae ; with these 

 are sooner or later associated at first a single, and afterwards 

 several rows of set^ on the inner margin of the upper end of 

 the joints, and finally, on the last joints, a dense irregular coat 

 of setge which often covers a great part of the inner surface. 

 On the inner branch the sette 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 uninjm'ed ; 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 

 four pairs of setse, but frequently only three in the fourth pair 

 of 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 

 vveaker (fig. 22). 



The fifth pair of feet is distinguished by a strong, some- 

 Avhat curved tooth, directed upwards, which stands at the com- 

 mencement of the dorsal surface of the second peduncular 

 joint ; 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. 



