72 DROPS OF WATER. 



they are found to glide slowly along at the 

 bottom of the water, in a straight line, though oc- 

 casionally a little slightly zigzag, as if to avoid 

 the roughness of the glass ; then, when anything 

 obstructs their path, they do not go round it, but 

 immediately turn back on almost the same track, 

 without turning the body, and this motion I 

 have seen a specimen keep up for some time : a 

 little tap on the glass will arrest their progress, 

 and then they immediately reverse their motion. 

 When, however, they meet with a substance which 

 may afford them food, they stop, and either glide 

 under or about it. They appear to have cilia 

 at the sides, for I have often observed small sub- 

 stances propelled along the body of the creature, 

 and even running backwards and forwards several 



