360 NATURAL THEOLOGY. 



in and propelled ; but the more curious action is 

 that of the cilia, or filannents, with which their 

 tentacula are covered. These cilia have a mo- 

 tion which produces a vortex in the fluid, and 

 tends to convey the floating nourishment towards 

 the mouth.* 



This well-attested fact leads us to comprehend 

 the phenomenon which is the principal object of 

 this note, and explains what is meant by "ciliary 

 motions." It is here necessary to mention that 

 what anatomists term the mucous membrane is 

 the lining of all those tubes and cavities of the 

 animal body which open outwardly, in contradis- 

 tinction to the membranes which line the proper 

 cavities of the body, and which are called serous 

 membranes. It is of itself a circumstance tend- 

 ing to the support of the conclusions to which the 

 whole arguments of this book point, that the fluids 

 thrown out to lubricate these surfaces are various 

 and appropriate to the nature of the cavity. The 

 nrembrane which is continuous all around, and 

 has no outlet, must be moistened by a fluid which 

 is to be absorbed again ; but the surface of the 

 cavity which has an outlet is moistened by a fluid 

 which is to be discharged as from an emunctuory. 



This brings us to the fact above referred to, 

 which, if the observation has been correctly made, 



♦ Spallanzani. 



