64 BALANIDjE. 



almost compared to the heaving of a man's chest. More- 

 over, the branchiae on each side are attached so closely to 

 the spur of the tergum, that each time the latter is moved, 

 the whole branchia must, I think, be agitated, and the 

 folds opened, as by the action of a lever. 



In our two commonest, tidal, sessile Cirripedes, viz. 

 Balanus balanoides and Chthamalus stellatus, I have ob- 

 served that, when left uncovered by water, they kept the 

 orifice of their operculums a little open, with a bubble of air 

 within their sacks, so that the orifice was in fact closed by 

 a thin septum of water, with air beneath ; when disturbed, 

 they closed their operculums with force, and expelled the 

 bubble of air with a clicking noise, which has been noticed by 

 Dr. Coldstream,* and has been thought to be made by the 

 movement of the operculum itself. Bed. crenatus, a deep- 

 water species, when out of water, keeps its operculum 

 closed. 



In Coronula, Platylepas, Tubicinella, and Xenobalanus, 

 each branchiaf consists of two unequal folds, both plicated 

 on both sides : in the two latter genera, they extend 

 far down the deep and elongated sacks, and hence the 

 area of surface altogether gained is extremely great. In 

 most of the species of Chthamalus, the branchia consist of 

 a small fillet barely plicated : in the allied Chamcesipho 

 coliimna, they are rudimentary, forming a smooth little 

 pouch only —th of an inch in length : in Chthamalus 

 scabi'osus they are quite aborted, being perhaps represented 

 by a slight hairy ridge ; but in Chthamalus dentatus, and 

 therefore within the limits of the same genus, the branchiaa 

 (and this seems to me a singular fact) are large, each being 

 composed of two plicated folds, as in Coronula. Tapering fila- 

 ments situated near the bases of the cirri, such as those occur- 

 ring in several species of the Lepadidae, are not found in any 

 sessile Cirripede ; but I have observed nearly similar filaments, 

 projecting upwards and inwards "at the base of the sack, in 

 several species of Balanus and in Coronula; those which I 



* ' Encyclopedia of Anatomy and Physiology ;' article Cirrhopoda. 



f Burmeister has given a good figure (Tab. 2, fig. 10) of the branchiae of 

 Coronula, (but the two folds are shaded too unequally), in his ' Beitrage zur 

 Naturgeschichte der Rankenfusser.' 



