PARAMCECIUM. 87 



tached by a thin stalk to the stalk of some weed or other object. 

 Besides the ciliary movement we here find that the general mass 

 of the protoplasm can suddenly and forcibly contract, so as to 

 completely alter its shape, and change the bell into a rounded 

 mass. This spasm of the body is commonly associated with a 

 wonderfully rapid contraction of the stalk. This stalk consists 

 of a delicate transparent sheath, in the centre of which is a thin 

 thread of pale protoplasm. The rapid contraction of the proto- 

 plasm of the stalk and the spasm of the bell occur on the appli- 

 cation of the least mechanical excitation, such as a touch to the 

 cover-glass. Here in a single cell we have certain portions set 

 apart for special purposes, most of which are the same as in para- 

 moecia. But the animal being attached requires a special way of 

 escaping from its enemies, and hence we find it endowed with 

 three special forms of motion. Besides the ciliary and stream- 

 ing protoplasmic motion, its body can spasmodically change its 

 shape, and the stalk contracts with a velocity comparable with 

 that of the most specially modified contractile tissue (muscle) of 

 the higher animals, by means of which their rapid and varied 

 movements are carried out. 



