182 DESCRIPTION OF {Polygastrica. 



one to consider them as plants ; but the following circum- 

 stance, which is of very considerable interest, militates 

 against it. In many Naviculse, it it observed that the 

 molecules, such as of indigo or carmine, &c., in the same 

 solution, that may come into contact with the surface of 

 the body of the creature, are immediately set in motion, 

 and often run along with considerable rapidity by the side 

 of the body, and even turn and run in an opposite 

 direction. This remarkable appearance has its cause, 

 perhaps, in the existence of numerous delicate cilia, which 

 are present over the surface of the creature, and giving 

 rise to the motion. 



" With our present instruments we cannot take cog- 

 nizance of these organs ; but when making use of a very 

 high power, a sort of transparent narrow zone is observed 

 around the bodies of the Bacillaria, 



" Lastly, Ehrenberg adduces another observation as 

 satisfactorily proving the animal nature of the Bacillaria. 

 They sometimes receive colouring matter, which fills the 

 vesicles looked upon by him as stomachs. This last state- 

 ment appears at least very striking, but the way in which 

 the case stands seems to be somewhat different. In the 

 first place, I can see no stomach sacs in the Naviculse, and 

 never observed in the living and moving Bacillaria the 

 colouring matter received at one extremity and carried 

 towards the centre, where these stomach sacs should lie, 

 whilst in the Infusoria such observations are easy; on 

 the other hand, it is not rarely found, especially with 

 the larger living animalcules, that the molecules of the 

 colouring matter employed lie upon the middle of the 

 broad ventral surface, from which it appears as if the colour- 



