230 THE MICROSCOPE AND ITS LESSONS. 



the cilia in motion round the head of melicerta to one 

 of those circular ventilators which used to be seen in 

 one of the upper panes of a kitchen window, running 

 round and round for the cure of smoky chimneys. One, 

 to whom I am greatly indebted for much of my little 

 knowledge of natural history, told me that he had re- 

 moved one of the "bricks," or small pellets, and that 

 immediately another was moulded from the inside the 

 whole process being revealed by the transparency of the 

 creature's body and deposited in its place by what 

 looked like the first finger and thumb of a man's hand, 

 both working together in the moulding of the " bricks." 



The vorticella is very much less in size than the 

 melicerta, but has similar interest for us in the wonderful 

 construction of its infinitely little transparent body. The 

 " tail " of the old author is in truth a long flexible stalk, 

 one end being attached to the stem or leaves of an 

 aquatic plant, commonly called " lemna," or duck-weed, 

 through the entire length of which runs the muscular 

 thread, the discovery of which, in one of my earliest 

 examinations, required a magnifying power of about a 

 million of times superficial. " When in activity and 

 secure from danger," says Mr. Hogg, from whose very 

 useful volume some of the foregoing has been taken, " the 

 little vorticella stretches its stalk to the utmost, whilst its 

 fringe of cilia is constantly drawing to its mouth any 

 luckless animalcule that may come within the influence 

 of the vortex it creates ; but at the least alarm the cilia 

 vanish, and the stalk, with the rapidity of lightning, draws 

 itself up into a little spiral coil." 



How often have I been astonished at witnessing the 

 extreme sensitiveness of this inhabitant of the invisible 

 world ! Simply by tapping the instrument, while the 

 little thing is hunting for its food, it withdraws itself 



