CIRRI. 83 



the segments of the posterior cirri; they are, also, espe- 

 cially in the genus Balanus, frequently produced in their 

 upper, ante-lateral corners, into remarkable prolongations 

 (see PL 29, fig. 4, of the third cirrus of Bal. perforalus), 

 clothed on their inner surfaces, and at their extremities, by 

 numerous bristles. The number of the segments in each 

 cirrus is in some degree variable, and increases with age ; 

 this is likewise the case, to a certain extent, with the 

 number of the spines borne on each segment. 



As compared with ordinary Crustaceans, I presume the 

 two rami answer to the " tige" and " palpe' of Milne 

 Edwards ; and the pedicel (as I have called it) to the two 

 basal segments of the leg.* The "fouet" or flabellum 

 does not appear to be developed in any Cirripede ; for 

 though the filamentary appendages in certain genera of 

 Lepadidae, might at first be thought to be of this nature, 

 yet their usual position beneath the basal articulation of the 

 first pair of cirri, and the occasional presence of more than 

 one, proves, I think, that such is not the case. 



Though the structure of the cirri is very uniform, yet we 

 meet with some peculiarities. In Chelonobia, the segments 

 of the posterior cirri bear only two pairs of main spines ; 

 whereas in some varieties of Balanus balanoides, they carry 

 as many as ten pair in a longitudinal row ; but in this latter 

 species, the number of these spines varies, in a singular 

 manner, from six to ten pairs. In Tubiciuella, the pairs of 

 spines on the segments of the posterior cirri are arranged 

 so closely one under the other, that they appear almost like 

 a single transverse row. Considering the whole family, the 

 third pair of cirri differs most in structure in the different 

 genera. Thus, in Chthamalm antennatus, the anterior (or 

 outer) ramus (PL 29, fig. 3) is thicker and much longer 

 than the posterior (or inner) ramus ; the number of the 

 segments in one instance being, in the two rami, 53 and 18 ; 

 in the longer ramus, the spines are arranged abnormally, 

 tending to form a little circle round each segment ; and 



* According to this author's new nomenclature, the pedicel would consist of 

 the coxopodite and basipodite ; the tige would be the ischiopodite and follow- 

 ing segments ; and the palpe would be the exopodite ; the epipodite or flabellum 

 being absent. (' Annales des Sciences Naturelles, 5 torn, xviii, 1852.) 



