THE WHEEL-ANIMALCULE. 77 



spicula, having a nimble and continual vibrating motion upwards and 

 downwards ; whereby the water becomes greatly agitated, and is brought 

 to the animal from several times the distance of its own length. As the 

 creature is capable of thrusting out these wheels, or drawing them in as 

 snails do their horns, the figure of them is different in their several degrees 

 of extension or contraction, or according to their position to the eye of 

 the observer*." 



RESUSCITATION OF THE INFUSORIA. Allusion has 

 already been made to the extraordinary tenacity of life 

 with which certain species of Infusoria are endowed, 

 a phenomenon which did not escape the notice of the 

 early microscopists. That the eggs of the oviparous 

 kinds should be found capable of development for a 

 long period after their exclusion, would not excite 

 much surprise ; but that adult animals, possessing eyes, 

 muscles, nerves, organs of respiration, &c., should revive 

 after being dried up to dust, is a phenomenon so start- 

 ling, as to require the most satisfactory evidence, before 

 the possibility of such a resurrection could be admitted. 

 The statement, with some limitation, is however un- 

 questionably true ; for though it is not to be supposed 

 that any animal could revive if it were quite dried up, 

 yet it is certain that some species of the Infusoria will 

 remain in a dormant state for years, if buried in earth 

 or sand apparently dry. Some Rotifers were alter- 



* Baker on the " Employment for the Microscope," pp. 269277. 



