168 VIGXETTES FROM INVISIBLE LIFE. 



than a change in position is effected. One pipe 

 makes a forward movement, followed by the next, 

 and next, throughout the entire series, until an 

 almost straight and rigid rod-like form is pro- 

 duced ; then a pause, and a backward movement is 

 begun, while the hindermost is at the same time 

 moving forward, so that each half of the row is 

 moving parallel to the other in opposite directions, 

 the centre remaining stationary. Now an impedi- 

 ment is encountered and pushed aside ; by-and-by 

 another which cannot be moved comes in the way, 

 and then the whole line of Diatoms pauses, but 

 only just so long as the forward movement would 

 have taken, and then they return. Again and 

 again is the journey attempted, and as often foiled 

 half way by this obstacle, yet there is no swerving, 

 no turning aside for another path, no giving up 

 the endeavour. Our patience is, however, exhausted, 

 and so we lift the thin glass cover, and with a fine 

 needle " clear the road " for our persevering 

 acquaintance. The movement is slow but regular, 

 and never did stage coach keep better time than 

 our Bacillaria Paradoxa.. 



The cause of this, and of the movements 



