ANATOMY OF THE LAMELLIBRANCHIATA. 299 



considered the rotation caused by the vibratile cilia in the 

 ova of the Acephala to be caused by a species of Vibrio get- 

 ting into the interior of the embryo, and feeding upon it. — 

 The latter has given figures of this supposed animalcule in 

 its different stages of growth, and his representation is merely 

 that of a branchial process. The author of these pages has 

 noticed that the hydroferous vessels of the Beroe, and of other 

 Radiata, are internally covered with cilia. He has not been 

 able to find them at all in any crustaceous or cirrhopodous 

 animal ; nor in the water-breathing larvae of insects. Dr. 

 Sharpey observed them on the branchiae of the Patella and 

 Chiton, and on those of the Annelides. He was unable to 

 see them in the Tunicata ; but he might have done so by the 

 aid of a more powerful lens, covering the meshes of the bran- 

 chial cavity ; they are remarkably small in these animals. — 

 On the branchiae of the Cephalopoda the author, though he 

 has had every facility of investigation, has not found these 

 organs, so general in water-breathing animals ; if they exist 

 there, they are particularly minute. They are present in the 

 Actiniae on the stomach and branchial cavity ; and remarkable 

 on the thread-like bodies dependant from the sides of the Act. 

 plumosa. In the Annelides they are only partially found. — 

 Their use being to excite currents in the water, they are, per- 

 haps, only found when there is no muscular apparatus to an- 

 swer that end. These cilia vary in size ; sometimes, invi- 

 sible with a lens of T \j. of an inch focus, they may, occasion- 

 ally, be discerned with one of weak power, or even by the 

 naked eye. 



The piercing or excavation of rocks, wood, &c, by these 

 animals, has been the subject of some dispute, as to the mode 

 in which it is performed ; and from the ravages committed 

 by them on shipping, &c, is a matter of interest. 1 Some 

 writers, as Montague, 2 Turton, 3 and Osier, 4 doubting the 

 possibility of its being effected by the action of the extremi- 

 ties of the valves, moved by the muscles of the animal, have 

 supposed the secretion of a solvent fluid. Were the exist- 

 ence of organs which might secrete it demonstrated, it is not 

 probable that a fluid capable of dissolving so many different 

 substances, — rocks of different compositions, wood, lava, ma- 

 drepores, &c, — could be formed ; or, if so, act on the sur- 

 rounding bodies without injuring the shell of the animal. — 

 Others, as Reaumur, 5 Argenville, 9 &c. have believed that the 



1 Blondel, sur les Lithodomes, Mem. Acad. Sci. Par. t. i. Parsons, Phil. 

 Trans, vol. xv. Rousset, sur les Tarets, 1733. Sellius, Hist. Tered. 1733 



2 Linn. Trans. 3 Conchological Dictionary. 4 Phil. Trans. 1826. 



5 Mem. Acad. Sciences, 1710. 6 Id. loc. 1712. 



