THE SIMPLEST LIVING THINGS 207 



The kinds with a firm or tough surface to the cell- 

 protoplasm and a permanent mouth and gullet leading 

 into the cell-substance have very usually a single large 

 lashing-whip (Flagellata), which drives them through 

 the water in search of prey, or they are clothed with 

 hundreds of such lashing threads of smaller size the 

 " cilia " described above (p. 195) arranged in rows or 

 circles, whence these animalcules are called " Ciliata." 

 The ciliates or one-celled animals are enabled by their 

 cilia to move with all the grace, variety, facility, and 

 apparent intelligence of the highest animals, and also to 

 create powerful vortex-currents by which food particles 

 are driven into the cell-mouth. 



It is a most remarkable and thought-stirring fact 

 that here we have " animalcules " which are no more 

 than isolated units of the kind and structure which go by 

 hundreds of thousands to build up a larger animal just 

 as bricks are units of the kind which to the number of 

 many thousands build up a house. And yet each of 

 these free-living units has a complete organisation 

 mouth, pharynx, renal organ, locomotive organs, and so 

 on similar in activity and general shape to the system 

 of large, capacious organs built up by the agglomeration 

 of millions of cell-units to form the body of a higher 

 animal. It is as though a single brick were provided 

 with door, windows, staircase, fireplace, chimneys, and 

 wine-cellar ! It is clear that there is only a resemblance 

 and not an identity of origin between the organs of the 

 multicellular animal and those of the single-celled 

 animalcule. The history of the growth of an animal 

 from the single egg-cell, and also the series of existing 

 many-celled animals, leading from simple forms to the 

 most complex, proves this. And in view of that fact 

 the wonderful elaboration of these diminutive creatures 

 many of them so small as to be absolutely invisible 



