ORGANS OF RESPIRATION. 525 



gonia, ten in alcyonium gelatinosum, fourteen in cellaria avi- 

 cularia, twenty- two in flustra carbesia, and higher numbers 

 in alcyonella, tubularia, caryophyllia, actinia, where they 

 form two or more series around the mouth. In some polypi- 

 phera, as lobularia, pennatula, gorgonia, where the large ten- 

 tacular cilia are not vibratile organs, the respiratory currents 

 and food are directed to the mouths of the polypi, by the 

 minute vibratile cilia which line the buccal and gastric cavi- 

 ties. So that the whole interior of the polypi, and their 

 prolonged tubular canals, are aerated by the ciliary currents 

 of the surrounding element, in the minutest compound zoo- 

 phytes, as in the larger isolated forms of actinise. 



The large fin-like vibratile cilia of beroe and other 

 ciliograde acalepha, disposed in symmetrical longitudinal 

 columns, and serving as organs of locomotion, like those 

 of polygastrica, must also contribute to the respiratory 

 function, by constantly renewing the stratum of water in 

 contact with the thin pellicle covering the exterior of their 

 soft body. These organs, however, are not branchial la- 

 mellee, destined to support the ramifications of blood ves- 

 sels, as in Crustacea and fishes. In the empty state of 

 the alimentary canal, the currents of water directed over 

 its ciliated surface, passing straight through the axis of 

 the body, will likewise aerate the mucous lining of that pas- 

 sage, as in polypi, and even in fishes. In the gaseous 

 swimming vesicles of the physograde species, as the physalia, 

 we already observe the analogue of the air-sac of fishes, and 

 the first rudiment of the lungs of higher vertebrata, although 

 they are not yet subservient to aerial respiration. In many 

 of the palliograde species, as aurelia, the four ovarial sacs 

 opening around the stomach, below the mantle, and sepa- 

 rated from the gastric cavity by thin septa, appear to extend 

 the respiratory surface ; but the greatest respiration of these 

 animals is probably effected by the vascular and active peri- 

 pheral margin of the mantle, and by passing currents of the 

 surrounding element through the whole ciliated interior of 

 their body, as seen when they are placed alive in sea water 

 artificially coloured. 



More distinct and more complex organs are appropriated to 

 the function of respiration in the echinoderma than in any other 

 radiata, which accords with the higher development of all 

 their other organs. In the asterias, the upper surface of the 



