THE POLYGASTRIA, 51 



have been observed in fifty species : the colour, or pig- 

 ment, is in most instances red, but in one genus it is 

 black. 



The Polygastria, when examined at night, are found 

 to be moving as actively as in the day ; in fact, they 

 seem never to require repose ; a phenomenon difficult 

 to be explained, unless we assume that their actions are 

 automatic, or involuntary. 



In the next division of animalcules, we shall find a 

 marked difference, both in structure and habits. The 

 increase of the species is no longer effected by spon- 

 taneous division or fissuration ; the organs of digestion 

 are less numerous, and of a higher type; and, though 

 locomotion is performed by cilia, the position and ar- 

 rangement of these instruments are considerably modi- 

 fied. 



