PHENOMENA IN THE ANIMAL BODY. 359 



which we are contemplating : and this we state, 

 to do away with those speculations which men 

 are prone to indulge in, when they suppose that 

 they have at last attained a sight, in these active 

 molecules, of the ultimate particles which consti- 

 tute the framework of animals.* 



Another class of facts drawn from the minute 

 world is no less wonderful than the motion of 

 these " active molecules :" we allude to certain 

 vibratory motions, or, as they are termed, ciliary 

 motions, on the mucous surfaces of animals. They 

 are somewhat analogous to the actions of the ro- 

 tatory apparatus of some of the infusoria. Both 

 the respiration and the prehension of food in 

 these animals are accomphshed by an influence 

 of their bodies, whereby a current is kept up in 

 the surrounding fluid ; a fresh stream by this 

 means plays over the apparatus of their respira- 

 tory organs, whilst in some the minute particles 

 of nutritious matter in the fluid are brought in 

 contact with their prehensile organs. 

 , The soft aquatic animals, called porifera, have 

 many orifices on their surface, into which the sur- 

 rounding fluid is drawn, and being then brought 

 into a common sac, it is expelled through a larger 

 central mouth.f We can conceive an action of 

 these pores, by which the water may be sucked 



* Animalcules are visible in the microscope, so minute, that 

 it is estimated that a million of them do not exceed in magnitude 

 a grain of sand. 



t Dr. Grant. 



