OF MICR O- OR GANISMS. 19 



they find themselves in a liquid; they frequently ex- 

 hibit a movement of oscillation which sometimes car- 

 ries them forward, sometimes backwards. An attempt 

 has been made to explain these movements by postu- 

 lating the presence of organs of locomotion, extremely 

 slender filaments planted at one of the extremities of 

 the Bacteria like small rods; but the existence of these 

 organs has not been absolutely proved. Even more 

 obscure is the movement observed in certain Grega- 

 rines. It would seem that in the case of these ani- 

 mals, which are often of considerable size, one ought 

 to be able to understand the principle of their move- 

 ments much more easily than in the case of such 

 small beings as the Bacteria; but this is not the case. 

 The Polycystids have a very peculiar manner of mov- 

 ing; the motion is one of perfect translation, uniform 

 and rectilinear; the animal seems to slide all of a 

 piece over the object-plate; it can go to the right, to 

 the left, stay its motion and resume it again; it is free 

 in directing its movements. Now, during this move- 

 ment nothing can be seen to take place in the body 

 from within or without. An analogous phenomenon 

 is to be observed in the Diatomes. Some scientists 

 have wished to explain the mysterious motion by 

 translation executed by the Gregarines, as being due 

 to an imperceptible undulation of the sarcode; but if 

 there were any undulations whatever, one ought to ob- 

 serve a correlative movement in the granules inside; 

 now this is something that is never seen. 



Thus there still exists a great deal of obscurity 

 concerning the principles determining motion among 

 the Proto-organisms. The theories based upon muscular 

 contraction that have been propounded from observ- 

 ing higher animals, are by no means sufficient to ex- 



