CHAPTER LXVIII 

 PROTECTIVE MOVEMENTS 



406. Contractions. Contraction under stimulation is a com- 

 mon thing among living beings. When the ameba is disturbed 



FIG. 177. Contraction of sea anemone 



When disturbed, the surface of this animal becomes greatly reduced by repeated 

 contractions, until it resembles a wart on a rock 



in any one of several ways, it immediately contracts. The 

 effect of this contraction may be protective in several ways : 



FIG. 178. The pill bug 



When suddenly disturbed, this animal curls up, thus reducing its exposed surface and 

 concealing its most delicate and sensitive parts 



1 . It reduces the total amount of surface exposed to danger. 



2. It hardens (condenses) the exposed surface. 



3. It withdraws the animal from the point of attack. 



360 



