VORTICELL^. 35 



freely swimming about. Notwithstanding the simi- 

 larities here stated, the appearance of certain of the 

 species is as various as it is curious. One of the 

 commonest species of the Infusoria (Paramecium 

 caudatum) is shaped somewhat like a grain of rice, 

 with a piece chipped out on one side, near the ex- 

 tremity of its body. It swims about with its un- 

 chipped extremity foremost, rotating as it goes. 

 During the milky condition of the water (before 

 alluded to), these creatures swarm to such a degree, 

 that a single drop of the fluid, when placed under 

 the microscope, appears filled with a dense cloud of 

 dancing midges. Another (Kerond silurus) may be 

 said to resemble a coffee-bean, with a host of cilia, 

 or short bristles, on the flat side. These are used 

 when swimming or running. But perhaps the most 

 singular and beautiful of all the infusorial animalcules 

 are the Vorticellce, which resemble minute cups or 

 flower-bells, mounted upon slender retractile thread- 

 like stalks, by which they are moored to the surface 

 of the weeds and stones. They are called Vorticeilae 

 on account of the little vortices or whirlpools which 

 they continually create in the water, by means of a 

 fringe of very minute cilia placed round the brim of 

 their cups. These cilia are so minute as to require 

 a very high microscopic power to make them 

 visible, and even then they are not easily detected, 

 on account of their extremely rapid vibration, which 

 never relaxes while the animal is in full vigour. On 



