II. — On some Phenomena connected with the Movement of 

 the Cilia in the common Mussel, (Mytilus edulis). By John 

 Quekett, Esq., Assistant Conservator of the Museum of the 

 Royal College of Surgeons of England. 



(Read April 17, 1845). 



Of all the various objects presented to us by the aid of the micro- 

 scope, none perhaps exceed in beauty and arrangement the phenome- 

 non that has been termed ciliary movement, which is found to occur 

 in more or less abundance throughout the whole of the various classes 

 of animals both of the vertebrate and invertebrate series. No one can 

 have witnessed this movement without having been struck with asto- 

 nishment at its great beauty, and at the same time having been led to 

 wonder by what species of mechanism such extraordinary effects 

 could be produced. 



As various as are these movements, so in like manner various have 

 been the speculations on the probable use of such a series of organs 

 ts cilia. By some authors their movement has been attributed to a 

 nagnetic or electrical force, while one author in particular, viz., 

 Laspail, has even gone so far as to deny the existence of cilia, and to 

 attribute their appearance to an optical illusion. 



The motion of cilia appears first to have been discovered in the 

 Infusoria. Leuwenhoek may be said to have first noticed them ; 

 he mentions their occurrence in a species of Volvox, and recognizes 

 their use. Our countryman Baker, in the year 1744, described them 

 wiih tolerable accuracy in the wheel animalcule, and made a distinc- 

 tioi between their rotatory and vibratile motions. Since then they 

 hare occupied the attention of Needham, Spallanzani, Otto Frederic 

 Miller, and many other observers ; but the great improvements which 

 ha T e been made in the microscope within the last few years, have 

 led to the conviction that there is scarcely an animal in which the 

 presence of cilia cannot be ascertained : and we are indebted to Mr. 

 Lister, Dr. Grant, and to Dr. Sharpey in particular in this country, 

 aid to Purkinje and Valentin abroad, for nearly all that we know of 

 tlis interesting subject. 



In some animals, the cilia may be seen investing the whole outer 

 sirface of the body ; in others they are confined to the edges ; and 



