These cirripedes have no branchiae, the whole surface of the body and of the sack, together with the small frena, serving for respiration. 查尔斯·达尔文.物种起源.
The ovigerous frena of certain cirripedes, which have ceased to give attachment to the ova and are feebly developed, are nascent branchiae. 查尔斯·达尔文.物种起源.