MECHANICAL MOVEMENTS IN CELLS. 79 



a board, any light bodies placed in contact with the ciliated surface of 

 the membrane will be moved comparatively rapidly forward in the 

 direction of oscillation of the cilia; or if the body of the frog is bisected, 

 and a glass tube passed in the mouth and out the oesophagus, which is 

 cut off at the point where it enters the stomach, the motion of the ciliated 

 epithelium lining the pharynx and oesophagus will be sufficient to cause 



Fig. 52.— Spermatozoa of Different Animals. (Thanhoffer.) 



P, b, a, spermatozoa of Paludina vivipura ; H», of Helix nemoralis ; B. of Blaps mortisaga ; B?', of 

 bull; V, of mole; K, of dog; D, of bat; Em, of man; E. of mouse ; C, of canary -bird ; Lot horse; Va.o, 

 of rat, ivit.li spermatoblasts; J, of sheep: Br, of frog; K. of Raja batis ; P«, n, spermatoblasts. 



the body of the frog to advance at a comparatively rapid rate, — as 

 much possibly as one millimeter in the second, or even more. It has been 

 estimated that, in oblique or vertical upward movements, each square 

 centimeter of ciliated membrane can perform in one hour 6.8 gramme 

 millimeters of work, or the cells can lift their own weight more than four 

 meters high (Bowditch). This motion of bodies placed in contact with 



