CIRRI. 81 



is a longitudinal medial suture in this expanse of mem- 

 brane, which I suppose indicates the lateral confluence of 

 the middle segments of the two outer maxillae. A short, 

 transverse articulation or fold separates this middle seg- 

 ment (fig. 4, a 1) of each maxilla from the third or basal 

 segment ; and this latter {a 2) is separated from the 

 body by a very distinct fold, which (at least amongst 

 the Lepadidae) sends inwards a short, medial, tongue- 

 formed apodeme. Here, then, we apparently have, as in 

 the mandibles, two segments under the upper free segment 

 of each outer maxilla, laterally confluent with the adjoining 

 organs. But I must state that, in old specimens, and only 

 in old specimens of Coronula diadema, I have found under 

 the outer maxilla an additional transverse ridge and fold, 

 which plainly shows how easily a mere thickening of the 

 membrane might be mistaken for an articulation. I can, 

 however, hardly persuade myself that the articulated mem- 

 brane, under the free part of the mandibles, which has now 

 been figured and described, has no homological signifi- 

 cation ; and the fusion of the palpus and labrum seems 

 too plain to be mistaken. Hence I must conclude that the 

 mouth, in the Cirripedia, does truly exhibit a compounded 

 structure of a very peculiar nature. 



Cirri. 



There are always six pair ; each biramous and multiarti- 

 culated, supported on a pedicel formed of two segments. 

 A shield -like swelling at the exterior bases of these pedicels 

 often appears like another segment ; but such, I believe, is 

 not its nature. The five posterior pairs answer to the five 

 pairs of ambulatory legs in the^ higher Crustaceans ; and 

 as in the case of the latter, the three, or the four hinder- 

 most pairs almost invariably .resemble each other. The 

 first pair, which is homologous with the outer maxillipeds 

 of ordinary Crustaceans, is separated by an interval from the 

 second pair ; — though this is not the case with the legs of the 

 pupa, from which the cirri are metamorphosed. These anterior 

 cirri are attached to the lateral edges of the mouth, namely to 

 the thickened rim of membrane, forming the supposed basal 



6 



