66 DIATOMS. 



board drawings were used to illustrate it. It was as fol- 

 lows : 



DIATOMS. 



BY D. B. WARD, M.D. 



About the end of the last century naturalists discov- 

 ered by the help of the microscope certain animalcules, 

 as they supposed, swimming about in the water and they 

 named them the bacillaria, by which name they are still 

 called by some Grerman and French writers, but are more 

 frequently known as the diatoms. They differ in several 

 respects from all other animalcules. Most of these little 

 organisms, at least the free-swimming ones, have one 

 grand aim and object in life, namely, to get something 

 to eat. They are exceedingly active and exceedingly 

 voracious. While these bacillaria were never seen to eat 

 anything, they swam about apparently on important 

 business which they did not visibly transact, but did 

 not eat. 



Then although in some species their motion is quite 

 rapid they have no perceptible organs of locomotion. 

 They have none of those little hair-like processes which 

 are called cilia or Jlagella with which so many of the 

 animalcules thrash their way through the water with 

 such marvellous speed that it is necessary to benumb 

 them with drugs or to thicken the water with syrup in 

 order to examine them at all. Nor have they any sy- 

 phons or collapsible organs to propel them forward by 

 ejecting a jet of water. I shall have more to say pres- 

 ently concerning their motion. Another peculiarity is 

 this : if you dry the drop of water in which they are 

 swimming instead of drying up to utter nothingness, as 

 is the case with infusoria, rotifers, etc., they retain their 

 shape and are found to have hard shells of silex, which 

 resist the action of intense heat so that they may be 



